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* [PATCH v1 2/2] WIP: Fix EEOP_JSON_CONSTRUCTOR and EEOP_JSONEXPR size.
@ 2022-06-17 01:33 Andres Freund <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Andres Freund @ 2022-06-17 01:33 UTC (permalink / raw)
Author:
Reviewed-By:
Discussion: https://postgr.es/m/
Backpatch:
---
src/include/executor/execExpr.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/src/include/executor/execExpr.h b/src/include/executor/execExpr.h
index 2fba1450c65..5bfa7e9bdd4 100644
--- a/src/include/executor/execExpr.h
+++ b/src/include/executor/execExpr.h
@@ -22,6 +22,8 @@ struct ExprEvalStep;
struct SubscriptingRefState;
struct ScalarArrayOpExprHashTable;
struct JsonbValue;
+struct JsonExprState;
+struct JsonConstructorExprState;
/* Bits in ExprState->flags (see also execnodes.h for public flag bits): */
/* expression's interpreter has been initialized */
--
2.35.1.677.gabf474a5dd
--rftf6si7y32exfgc--
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH 6/6] Use multiple snapshots to copy the data.
@ 2025-12-13 18:27 Antonin Houska <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Antonin Houska @ 2025-12-13 18:27 UTC (permalink / raw)
REPACK (CONCURRENTLY) does not prevent applications from using the table that
is being processed, however it can prevent the xmin horizon from advancing and
thus restrict VACUUM for the whole database. This patch adds the ability to
use particular snapshot only for certain range of pages. Each time that number
of pages is processed, a new snapshot is built, which supposedly has its xmin
higher than the previous snapshot.
The data copying works as follows:
1. Have the logical decoding system build a snapshot S0 for range R0 at
LSN0. This snapshot sees all the data changes whose commit records have
LSN < LSN0.
2. Copy the pages in that range to the new relation. The changes not visible
to the snapshot (because their transactions are still running) will
appear in the output of the logical decoding system as soon as their
commit records appear in WAL.
3. Perform logical decoding of all changes we find in WAL for the table
we're repacking, put them aside and remember that out of these we can
only apply those that affect the range R0 in the old
relation. (Naturally, we cannot apply ones that belong to other pages
because it's impossible to UPDATE / DELETE a row in the new relation if
it hasn't been copied yet.) Once the decoding is done, consider LSN1 to
be the position of the end of the last WAL record decoded.
4. Build a new snapshot S1 at position LSN1, i.e. one that sees all the data
whose commit records are at WAL positions < LSN1. Use this snapshot to
copy the range of pages R1.
5. Perform logical decoding like in step 3, but remember, that out of this
next set, only changes belonging to ranges R0 *and* R1 in the old table
can be applied.
6. etc
Note that the changes decoded above should not be applied to the new relation
until the whole relation has been copied. The point is that we need "identity
index" to apply UPDATE and DELETE statements, and bulk creation of indexes on
the already copied heap is probably better than retail insertions during the
copying.
Special attention needs to be paid to UPDATES that span page ranges. For
example, if the old tuple is in range R0, but the new tuple is in R1, and R1
hasn't been copied yet, we only DELETE the old version from the new
relation. The new version will be handled during processing of range R1. The
snapshot S1 will be based on WAL position following that UPDATE, so it'll see
the new tuple if its transaction's commit record is at WAL position lower than
the position where we built the snapshot. On the other hand, if the commit
record appears at higher position than the that of the snapshot, the
corresponding INSERT will be decoded and replayed sometime later: once the
scan of R1 started, changes of tuples belonging to it are no longer filtered
out.
Likewise, if the old tuple is in range R1 (not yet copied) but the new tuple
is in R0, we only perform INSERT on the new relation. The deletion of the old
version will either be visible to the snapshot S1 (i.e. the snapshot won't see
the old version), or replayed later.
This approach introduces one limitation though: if the USING INDEX clause is
specified, an explicit sort is always used. Index scan wouldn't work because
it does not return the tuples sorted by CTID. That way we wouldn't be able to
split the copying into ranges of pages. I'm not sure it's serious. If REPACK
runs concurrently and does not restrict VACUUM, the execution time should not
be critical.
A new GUC repack_snapshot_after can be used to set the number of pages per
snapshot. It's currently classified as DEVELOPER_OPTIONS and may be replaced
by a constant after enough evaluation is done.
---
src/backend/access/heap/heapam_handler.c | 144 ++++-
src/backend/commands/cluster.c | 561 +++++++++++++-----
src/backend/replication/logical/decode.c | 47 +-
src/backend/replication/logical/logical.c | 30 +-
.../replication/logical/reorderbuffer.c | 50 ++
src/backend/replication/logical/snapbuild.c | 27 +-
.../pgoutput_repack/pgoutput_repack.c | 2 +
src/backend/utils/misc/guc_parameters.dat | 10 +
src/backend/utils/misc/guc_tables.c | 1 +
src/include/access/tableam.h | 14 +-
src/include/commands/cluster.h | 65 ++
src/include/replication/logical.h | 2 +-
src/include/replication/reorderbuffer.h | 1 +
src/include/replication/snapbuild.h | 2 +-
src/tools/pgindent/typedefs.list | 3 +-
15 files changed, 771 insertions(+), 188 deletions(-)
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index cb09e6fd1dc..b87fad605e4 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -33,6 +33,7 @@
#include "catalog/index.h"
#include "catalog/storage.h"
#include "catalog/storage_xlog.h"
+#include "commands/cluster.h"
#include "commands/progress.h"
#include "executor/executor.h"
#include "miscadmin.h"
@@ -686,12 +687,12 @@ static void
heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
Relation OldIndex, bool use_sort,
TransactionId OldestXmin,
- Snapshot snapshot,
TransactionId *xid_cutoff,
MultiXactId *multi_cutoff,
double *num_tuples,
double *tups_vacuumed,
- double *tups_recently_dead)
+ double *tups_recently_dead,
+ void *tableam_data)
{
RewriteState rwstate = NULL;
IndexScanDesc indexScan;
@@ -707,7 +708,10 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
bool *isnull;
BufferHeapTupleTableSlot *hslot;
BlockNumber prev_cblock = InvalidBlockNumber;
- bool concurrent = snapshot != NULL;
+ ConcurrentChangeContext *ctx = (ConcurrentChangeContext *) tableam_data;
+ bool concurrent = ctx != NULL;
+ Snapshot snapshot = NULL;
+ BlockNumber range_end = InvalidBlockNumber;
/* Remember if it's a system catalog */
is_system_catalog = IsSystemRelation(OldHeap);
@@ -744,8 +748,9 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
* that still need to be copied, we scan with SnapshotAny and use
* HeapTupleSatisfiesVacuum for the visibility test.
*
- * In the CONCURRENTLY case, we do regular MVCC visibility tests, using
- * the snapshot passed by the caller.
+ * In the CONCURRENTLY case, we do regular MVCC visibility tests. The
+ * snapshot changes several times during the scan so that we do not block
+ * the progress of the xmin horizon for VACUUM too much.
*/
if (OldIndex != NULL && !use_sort)
{
@@ -773,10 +778,15 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
pgstat_progress_update_param(PROGRESS_REPACK_PHASE,
PROGRESS_REPACK_PHASE_SEQ_SCAN_HEAP);
- tableScan = table_beginscan(OldHeap,
- snapshot ? snapshot : SnapshotAny,
- 0, (ScanKey) NULL);
+ tableScan = table_beginscan(OldHeap, SnapshotAny, 0, (ScanKey) NULL);
heapScan = (HeapScanDesc) tableScan;
+
+ /*
+ * In CONCURRENTLY mode we scan the table by ranges of blocks and the
+ * algorithm below expects forward direction. (No other direction
+ * should be set here regardless concurrently anyway.)
+ */
+ Assert(heapScan->rs_dir == ForwardScanDirection || !concurrent);
indexScan = NULL;
/* Set total heap blocks */
@@ -787,6 +797,24 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
slot = table_slot_create(OldHeap, NULL);
hslot = (BufferHeapTupleTableSlot *) slot;
+ if (concurrent)
+ {
+ /*
+ * Do not block the progress of xmin horizons.
+ *
+ * TODO Analyze thoroughly if this might have bad consequences.
+ */
+ PopActiveSnapshot();
+ InvalidateCatalogSnapshot();
+
+ /*
+ * Wait until the worker has the initial snapshot and retrieve it.
+ */
+ snapshot = repack_get_snapshot(ctx);
+
+ PushActiveSnapshot(snapshot);
+ }
+
/*
* Scan through the OldHeap, either in OldIndex order or sequentially;
* copy each tuple into the NewHeap, or transiently to the tuplesort
@@ -803,6 +831,13 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
if (indexScan != NULL)
{
+ /*
+ * Index scan should not be used in the CONCURRENTLY case because
+ * it returns tuples in random order, so we could not split the
+ * scan into a series of page ranges.
+ */
+ Assert(!concurrent);
+
if (!index_getnext_slot(indexScan, ForwardScanDirection, slot))
break;
@@ -824,6 +859,18 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
*/
pgstat_progress_update_param(PROGRESS_REPACK_HEAP_BLKS_SCANNED,
heapScan->rs_nblocks);
+
+ if (concurrent)
+ {
+ PopActiveSnapshot();
+
+ /*
+ * For the last range, there are no restriction on block
+ * numbers, so the concurrent data changes pertaining to
+ * this range can decoded (and applied) anytime after this
+ * loop.
+ */
+ }
break;
}
@@ -922,6 +969,75 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
continue;
}
}
+ else
+ {
+ BlockNumber blkno;
+ bool visible;
+
+ /*
+ * With CONCURRENTLY, we use each snapshot only for certain range
+ * of pages, so that VACUUM does not get block for too long. So
+ * first check if the tuple falls into the current range.
+ */
+ blkno = BufferGetBlockNumber(buf);
+
+ /* The first block of the scan? */
+ if (!BlockNumberIsValid(ctx->first_block))
+ {
+ Assert(!BlockNumberIsValid(range_end));
+
+ ctx->first_block = blkno;
+ range_end = repack_blocks_per_snapshot;
+ }
+ else
+ {
+ Assert(BlockNumberIsValid(range_end));
+
+ /* End of the current range? */
+ if (blkno >= range_end)
+ {
+ XLogRecPtr end_of_wal;
+
+ PopActiveSnapshot();
+
+ /*
+ * XXX It might be worth Assert(CatalogSnapshot == NULL)
+ * here, however that symbol is not external.
+ */
+
+ /*
+ * Decode all the concurrent data changes committed so far
+ * - these will be applicable to the current range.
+ */
+ end_of_wal = GetFlushRecPtr(NULL);
+ repack_get_concurrent_changes(ctx, end_of_wal, range_end,
+ true, false);
+
+ /*
+ * Define the next range.
+ */
+ range_end = blkno + repack_blocks_per_snapshot;
+
+ /*
+ * Get the snapshot for the next range - it should have
+ * been built at the position right after the last change
+ * decoded. Data present in the next range of blocks will
+ * either be visible to the snapshot or appear in the next
+ * batch of decoded changes.
+ */
+ snapshot = repack_get_snapshot(ctx);
+ PushActiveSnapshot(snapshot);
+ }
+ }
+
+ /* Finally check the tuple visibility. */
+ LockBuffer(buf, BUFFER_LOCK_SHARE);
+ visible = HeapTupleSatisfiesVisibility(tuple, snapshot, buf);
+ LockBuffer(buf, BUFFER_LOCK_UNLOCK);
+
+ if (!visible)
+ continue;
+ }
*num_tuples += 1;
if (tuplesort != NULL)
@@ -956,6 +1072,18 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
}
}
+ if (concurrent)
+ {
+ XLogRecPtr end_of_wal;
+
+ /* Decode the changes belonging to the last range. */
+ end_of_wal = GetFlushRecPtr(NULL);
+ repack_get_concurrent_changes(ctx, end_of_wal, InvalidBlockNumber,
+ false, false);
+
+ PushActiveSnapshot(GetTransactionSnapshot());
+ }
+
if (indexScan != NULL)
index_endscan(indexScan);
if (tableScan != NULL)
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index b0383c1375f..3eb642b996d 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -110,38 +110,27 @@ typedef struct
RelFileLocator repacked_rel_locator = {.relNumber = InvalidOid};
RelFileLocator repacked_rel_toast_locator = {.relNumber = InvalidOid};
-/*
- * Everything we need to call ExecInsertIndexTuples().
- */
-typedef struct IndexInsertState
-{
- ResultRelInfo *rri;
- EState *estate;
-} IndexInsertState;
-
/* The WAL segment being decoded. */
static XLogSegNo repack_current_segment = 0;
/*
- * Information needed to apply concurrent data changes.
+ * When REPACK (CONCURRENTLY) copies data to the new heap, a new snapshot is
+ * built after processing this many pages.
*/
-typedef struct ChangeDest
-{
- /* The relation the changes are applied to. */
- Relation rel;
+int repack_blocks_per_snapshot = 1024;
- /*
- * The following is needed to find the existing tuple if the change is
- * UPDATE or DELETE. 'ident_key' should have all the fields except for
- * 'sk_argument' initialized.
- */
- Relation ident_index;
- ScanKey ident_key;
- int ident_key_nentries;
+/*
+ * Remember here to which pages should applied to changes recorded in given
+ * file.
+ */
+typedef struct RepackApplyRange
+{
+ /* The first block of the next range. */
+ BlockNumber end;
- /* Needed to update indexes of rel_dst. */
- IndexInsertState *iistate;
-} ChangeDest;
+ /* File containing the changes to be applied to blocks in this range. */
+ char *fname;
+} RepackApplyRange;
/*
* Layout of shared memory used for communication between backend and the
@@ -152,6 +141,9 @@ typedef struct DecodingWorkerShared
/* Is the decoding initialized? */
bool initialized;
+ /* Set to request a snapshot. */
+ bool snapshot_requested;
+
/*
* Once the worker has reached this LSN, it should close the current
* output file and either create a new one or exit, according to the field
@@ -159,20 +151,25 @@ typedef struct DecodingWorkerShared
* the WAL available and keep checking this field. It is ok if the worker
* had already decoded records whose LSN is >= lsn_upto before this field
* has been set.
+ *
+ * Set a valid LSN to request data changes.
*/
XLogRecPtr lsn_upto;
+#define WORKER_RESPONSE_SNAPSHOT 0x1
+#define WORKER_RESPONSE_CHANGES 0x2
+ /* Which kind of data is ready? */
+ int response;;
+
/* Exit after closing the current file? */
bool done;
/* The output is stored here. */
SharedFileSet sfs;
- /* Can backend read the file contents? */
- bool sfs_valid;
-
/* Number of the last file exported by the worker. */
- int last_exported;
+ int last_exported_changes;
+ int last_exported_snapshot;
/* Synchronize access to the fields above. */
slock_t mutex;
@@ -214,26 +211,14 @@ typedef struct DecodingWorkerShared
* the fileset name.)
*/
static inline void
-DecodingWorkerFileName(char *fname, Oid relid, uint32 seq)
+DecodingWorkerFileName(char *fname, Oid relid, uint32 seq, bool snapshot)
{
- snprintf(fname, MAXPGPATH, "%u-%u", relid, seq);
+ if (!snapshot)
+ snprintf(fname, MAXPGPATH, "%u-%u", relid, seq);
+ else
+ snprintf(fname, MAXPGPATH, "%u-%u-snapshot", relid, seq);
}
-/*
- * Backend-local information to control the decoding worker.
- */
-typedef struct DecodingWorker
-{
- /* The worker. */
- BackgroundWorkerHandle *handle;
-
- /* DecodingWorkerShared is in this segment. */
- dsm_segment *seg;
-
- /* Handle of the error queue. */
- shm_mq_handle *error_mqh;
-} DecodingWorker;
-
/* Pointer to currently running decoding worker. */
static DecodingWorker *decoding_worker = NULL;
@@ -250,11 +235,11 @@ static void check_repack_concurrently_requirements(Relation rel);
static void rebuild_relation(Relation OldHeap, Relation index, bool verbose,
bool concurrent);
static void copy_table_data(Relation NewHeap, Relation OldHeap, Relation OldIndex,
- Snapshot snapshot,
bool verbose,
bool *pSwapToastByContent,
TransactionId *pFreezeXid,
- MultiXactId *pCutoffMulti);
+ MultiXactId *pCutoffMulti,
+ ConcurrentChangeContext *ctx);
static List *get_tables_to_repack(RepackCommand cmd, bool usingindex,
MemoryContext permcxt);
static List *get_tables_to_repack_partitioned(RepackCommand cmd,
@@ -264,9 +249,12 @@ static bool cluster_is_permitted_for_relation(RepackCommand cmd,
Oid relid, Oid userid);
static LogicalDecodingContext *setup_logical_decoding(Oid relid);
-static bool decode_concurrent_changes(LogicalDecodingContext *ctx,
+static bool decode_concurrent_changes(LogicalDecodingContext *decoding_ctx,
DecodingWorkerShared *shared);
-static void apply_concurrent_changes(BufFile *file, ChangeDest *dest);
+static void apply_concurrent_changes(ConcurrentChangeContext *ctx);
+static void apply_concurrent_changes_file(ConcurrentChangeContext *ctx,
+ BufFile *file,
+ BlockNumber range_end);
static void apply_concurrent_insert(Relation rel, HeapTuple tup,
IndexInsertState *iistate,
TupleTableSlot *index_slot);
@@ -275,12 +263,14 @@ static void apply_concurrent_update(Relation rel, HeapTuple tup,
IndexInsertState *iistate,
TupleTableSlot *index_slot);
static void apply_concurrent_delete(Relation rel, HeapTuple tup_target);
-static HeapTuple find_target_tuple(Relation rel, ChangeDest *dest,
+static bool is_tuple_in_block_range(HeapTuple tup, BlockNumber start,
+ BlockNumber end);
+static HeapTuple find_target_tuple(Relation rel,
+ ConcurrentChangeContext *ctx,
HeapTuple tup_key,
TupleTableSlot *ident_slot);
-static void process_concurrent_changes(XLogRecPtr end_of_wal,
- ChangeDest *dest,
- bool done);
+static void repack_add_block_range(ConcurrentChangeContext *ctx,
+ BlockNumber end, char *fname);
static IndexInsertState *get_index_insert_state(Relation relation,
Oid ident_index_id,
Relation *ident_index_p);
@@ -291,7 +281,8 @@ static void cleanup_logical_decoding(LogicalDecodingContext *ctx);
static void rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap,
Relation cl_index,
TransactionId frozenXid,
- MultiXactId cutoffMulti);
+ MultiXactId cutoffMulti,
+ ConcurrentChangeContext *ctx);
static List *build_new_indexes(Relation NewHeap, Relation OldHeap, List *OldIndexes);
static Relation process_single_relation(RepackStmt *stmt,
LOCKMODE lockmode,
@@ -302,9 +293,8 @@ static Oid determine_clustered_index(Relation rel, bool usingindex,
static void start_decoding_worker(Oid relid);
static void stop_decoding_worker(void);
static void repack_worker_internal(dsm_segment *seg);
-static void export_initial_snapshot(Snapshot snapshot,
- DecodingWorkerShared *shared);
-static Snapshot get_initial_snapshot(DecodingWorker *worker);
+static void export_snapshot(Snapshot snapshot,
+ DecodingWorkerShared *shared);
static void ProcessRepackMessage(StringInfo msg);
static const char *RepackCommandAsString(RepackCommand cmd);
@@ -1008,6 +998,15 @@ check_repack_concurrently_requirements(Relation rel)
RelationGetRelationName(rel)),
(errhint("Relation \"%s\" has no identity index.",
RelationGetRelationName(rel)))));
+
+ /*
+ * In the CONCURRENTLY mode we don't want to use the same snapshot
+ * throughout the whole processing, as it could block the progress of xmin
+ * horizon.
+ */
+ if (IsolationUsesXactSnapshot())
+ ereport(ERROR,
+ (errmsg("REPACK (CONCURRENTLY) does not support transaction isolation higher than READ COMMITTED")));
}
@@ -1038,7 +1037,7 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose, bool concurrent
bool swap_toast_by_content;
TransactionId frozenXid;
MultiXactId cutoffMulti;
- Snapshot snapshot = NULL;
+ ConcurrentChangeContext *ctx = NULL;
#if USE_ASSERT_CHECKING
LOCKMODE lmode;
@@ -1050,6 +1049,13 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose, bool concurrent
if (concurrent)
{
+ /*
+ * This is only needed here to gather the data changes and range
+ * information during the copying. The fields needed to apply the
+ * changes be filled later.
+ */
+ ctx = palloc0_object(ConcurrentChangeContext);
+
/*
* The worker needs to be member of the locking group we're the leader
* of. We ought to become the leader before the worker starts. The
@@ -1075,13 +1081,7 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose, bool concurrent
* REPACK CONCURRENTLY.
*/
start_decoding_worker(tableOid);
-
- /*
- * Wait until the worker has the initial snapshot and retrieve it.
- */
- snapshot = get_initial_snapshot(decoding_worker);
-
- PushActiveSnapshot(snapshot);
+ ctx->worker = decoding_worker;
}
/* for CLUSTER or REPACK USING INDEX, mark the index as the one to use */
@@ -1105,21 +1105,25 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose, bool concurrent
NewHeap = table_open(OIDNewHeap, NoLock);
/* Copy the heap data into the new table in the desired order */
- copy_table_data(NewHeap, OldHeap, index, snapshot, verbose,
- &swap_toast_by_content, &frozenXid, &cutoffMulti);
-
- /* The historic snapshot won't be needed anymore. */
- if (snapshot)
+ if (concurrent)
{
- PopActiveSnapshot();
- UpdateActiveSnapshotCommandId();
+ ctx->first_block = InvalidBlockNumber;
+ ctx->block_ranges = NIL;
}
+ copy_table_data(NewHeap, OldHeap, index, verbose, &swap_toast_by_content,
+ &frozenXid, &cutoffMulti, ctx);
if (concurrent)
{
+ /*
+ * Make sure the active snapshot can see the data copied, so the rows
+ * can be updated / deleted.
+ */
+ UpdateActiveSnapshotCommandId();
+
Assert(!swap_toast_by_content);
rebuild_relation_finish_concurrent(NewHeap, OldHeap, index,
- frozenXid, cutoffMulti);
+ frozenXid, cutoffMulti, ctx);
pgstat_progress_update_param(PROGRESS_REPACK_PHASE,
PROGRESS_REPACK_PHASE_FINAL_CLEANUP);
@@ -1283,9 +1287,6 @@ make_new_heap(Oid OIDOldHeap, Oid NewTableSpace, Oid NewAccessMethod,
/*
* Do the physical copying of table data.
*
- * 'snapshot' and 'decoding_ctx': see table_relation_copy_for_cluster(). Pass
- * iff concurrent processing is required.
- *
* There are three output parameters:
* *pSwapToastByContent is set true if toast tables must be swapped by content.
* *pFreezeXid receives the TransactionId used as freeze cutoff point.
@@ -1293,8 +1294,9 @@ make_new_heap(Oid OIDOldHeap, Oid NewTableSpace, Oid NewAccessMethod,
*/
static void
copy_table_data(Relation NewHeap, Relation OldHeap, Relation OldIndex,
- Snapshot snapshot, bool verbose, bool *pSwapToastByContent,
- TransactionId *pFreezeXid, MultiXactId *pCutoffMulti)
+ bool verbose, bool *pSwapToastByContent,
+ TransactionId *pFreezeXid, MultiXactId *pCutoffMulti,
+ ConcurrentChangeContext *ctx)
{
Relation relRelation;
HeapTuple reltup;
@@ -1311,7 +1313,7 @@ copy_table_data(Relation NewHeap, Relation OldHeap, Relation OldIndex,
int elevel = verbose ? INFO : DEBUG2;
PGRUsage ru0;
char *nspname;
- bool concurrent = snapshot != NULL;
+ bool concurrent = ctx != NULL;
LOCKMODE lmode;
lmode = concurrent ? ShareUpdateExclusiveLock : AccessExclusiveLock;
@@ -1423,8 +1425,18 @@ copy_table_data(Relation NewHeap, Relation OldHeap, Relation OldIndex,
* provided, else plain seqscan.
*/
if (OldIndex != NULL && OldIndex->rd_rel->relam == BTREE_AM_OID)
- use_sort = plan_cluster_use_sort(RelationGetRelid(OldHeap),
- RelationGetRelid(OldIndex));
+ {
+ if (!concurrent)
+ use_sort = plan_cluster_use_sort(RelationGetRelid(OldHeap),
+ RelationGetRelid(OldIndex));
+ else
+
+ /*
+ * To use multiple snapshots, we need to process the table
+ * sequentially.
+ */
+ use_sort = true;
+ }
else
use_sort = false;
@@ -1453,11 +1465,11 @@ copy_table_data(Relation NewHeap, Relation OldHeap, Relation OldIndex,
* values (e.g. because the AM doesn't use freezing).
*/
table_relation_copy_for_cluster(OldHeap, NewHeap, OldIndex, use_sort,
- cutoffs.OldestXmin, snapshot,
+ cutoffs.OldestXmin,
&cutoffs.FreezeLimit,
&cutoffs.MultiXactCutoff,
&num_tuples, &tups_vacuumed,
- &tups_recently_dead);
+ &tups_recently_dead, ctx);
/* return selected values to caller, get set as relfrozenxid/minmxid */
*pFreezeXid = cutoffs.FreezeLimit;
@@ -2610,6 +2622,7 @@ decode_concurrent_changes(LogicalDecodingContext *ctx,
DecodingWorkerShared *shared)
{
RepackDecodingState *dstate;
+ bool snapshot_requested;
XLogRecPtr lsn_upto;
bool done;
char fname[MAXPGPATH];
@@ -2617,11 +2630,14 @@ decode_concurrent_changes(LogicalDecodingContext *ctx,
dstate = (RepackDecodingState *) ctx->output_writer_private;
/* Open the output file. */
- DecodingWorkerFileName(fname, shared->relid, shared->last_exported + 1);
+ DecodingWorkerFileName(fname, shared->relid,
+ shared->last_exported_changes + 1,
+ false);
dstate->file = BufFileCreateFileSet(&shared->sfs.fs, fname);
SpinLockAcquire(&shared->mutex);
lsn_upto = shared->lsn_upto;
+ snapshot_requested = shared->snapshot_requested;
done = shared->done;
SpinLockRelease(&shared->mutex);
@@ -2689,6 +2705,7 @@ decode_concurrent_changes(LogicalDecodingContext *ctx,
{
SpinLockAcquire(&shared->mutex);
lsn_upto = shared->lsn_upto;
+ snapshot_requested = shared->snapshot_requested;
/* 'done' should be set at the same time as 'lsn_upto' */
done = shared->done;
SpinLockRelease(&shared->mutex);
@@ -2710,28 +2727,108 @@ decode_concurrent_changes(LogicalDecodingContext *ctx,
*/
BufFileClose(dstate->file);
dstate->file = NULL;
+
+ /*
+ * Before publishing the data changes, export the snapshot too if
+ * requested. Publishing both at once makes sense because both are needed
+ * at the same time, and it's simpler.
+ */
+ if (snapshot_requested)
+ {
+ Snapshot snapshot;
+
+ snapshot = SnapBuildSnapshotForRepack(ctx->snapshot_builder);
+ export_snapshot(snapshot, shared);
+
+ /*
+ * Adjust the replication slot's xmin so that VACUUM can do more work.
+ */
+ LogicalIncreaseXminForSlot(InvalidXLogRecPtr, snapshot->xmin, false);
+ FreeSnapshot(snapshot);
+ }
+ else
+ {
+ /*
+ * If data changes were requested but no following snapshot, we don't
+ * care about xmin horizon because the heap copying should be done by
+ * now.
+ */
+ LogicalIncreaseXminForSlot(InvalidXLogRecPtr, InvalidTransactionId,
+ false);
+
+ }
+
+ /* Now announce that the output is available. */
SpinLockAcquire(&shared->mutex);
shared->lsn_upto = InvalidXLogRecPtr;
- shared->sfs_valid = true;
- shared->last_exported++;
+ shared->response |= WORKER_RESPONSE_CHANGES;
+ shared->last_exported_changes++;
+ if (snapshot_requested)
+ {
+ shared->snapshot_requested = false;
+ shared->response |= WORKER_RESPONSE_SNAPSHOT;
+ shared->last_exported_snapshot++;
+ }
SpinLockRelease(&shared->mutex);
+
ConditionVariableSignal(&shared->cv);
return done;
}
/*
- * Apply changes stored in 'file'.
+ * Apply all concurrent changes.
*/
static void
-apply_concurrent_changes(BufFile *file, ChangeDest *dest)
+apply_concurrent_changes(ConcurrentChangeContext *ctx)
+{
+ DecodingWorkerShared *shared;
+ ListCell *lc;
+
+ shared = (DecodingWorkerShared *) dsm_segment_address(decoding_worker->seg);
+
+ foreach(lc, ctx->block_ranges)
+ {
+ RepackApplyRange *range;
+ BufFile *file;
+
+ range = (RepackApplyRange *) lfirst(lc);
+
+ file = BufFileOpenFileSet(&shared->sfs.fs, range->fname, O_RDONLY,
+ false);
+
+ /*
+ * If range end is valid, the start should be as well.
+ */
+ Assert(!BlockNumberIsValid(range->end) ||
+ BlockNumberIsValid(ctx->first_block));
+
+ apply_concurrent_changes_file(ctx, file, range->end);
+ BufFileClose(file);
+
+ pfree(range->fname);
+ pfree(range);
+ }
+
+ /* Get ready for the next decoding. */
+ ctx->block_ranges = NIL;
+ ctx->first_block = InvalidBlockNumber;
+}
+
+/*
+ * Apply concurrent changes stored in 'file'.
+ */
+static void
+apply_concurrent_changes_file(ConcurrentChangeContext *ctx, BufFile *file,
+ BlockNumber range_end)
{
char kind;
uint32 t_len;
- Relation rel = dest->rel;
+ Relation rel = ctx->rel;
TupleTableSlot *index_slot,
*ident_slot;
HeapTuple tup_old = NULL;
+ bool check_range = BlockNumberIsValid(range_end);
/* TupleTableSlot is needed to pass the tuple to ExecInsertIndexTuples(). */
index_slot = MakeSingleTupleTableSlot(RelationGetDescr(rel),
@@ -2759,8 +2856,8 @@ apply_concurrent_changes(BufFile *file, ChangeDest *dest)
tup->t_data = (HeapTupleHeader) ((char *) tup + HEAPTUPLESIZE);
BufFileReadExact(file, tup->t_data, t_len);
tup->t_len = t_len;
- ItemPointerSetInvalid(&tup->t_self);
- tup->t_tableOid = RelationGetRelid(dest->rel);
+ tup->t_tableOid = RelationGetRelid(ctx->rel);
+ BufFileReadExact(file, &tup->t_self, sizeof(tup->t_self));
if (kind == CHANGE_UPDATE_OLD)
{
@@ -2771,7 +2868,10 @@ apply_concurrent_changes(BufFile *file, ChangeDest *dest)
{
Assert(tup_old == NULL);
- apply_concurrent_insert(rel, tup, dest->iistate, index_slot);
+ if (!check_range ||
+ is_tuple_in_block_range(tup, ctx->first_block, range_end))
+ apply_concurrent_insert(rel, tup, ctx->iistate,
+ index_slot);
pfree(tup);
}
@@ -2792,16 +2892,52 @@ apply_concurrent_changes(BufFile *file, ChangeDest *dest)
/*
* Find the tuple to be updated or deleted.
*/
- tup_exist = find_target_tuple(rel, dest, tup_key, ident_slot);
- if (tup_exist == NULL)
- elog(ERROR, "failed to find target tuple");
+ if (!check_range ||
+ (is_tuple_in_block_range(tup_key, ctx->first_block,
+ range_end)))
+ {
+ /* The change needs to be applied to this tuple. */
+ tup_exist = find_target_tuple(rel, ctx, tup_key, ident_slot);
+ if (tup_exist == NULL)
+ elog(ERROR, "failed to find target tuple");
- if (kind == CHANGE_UPDATE_NEW)
- apply_concurrent_update(rel, tup, tup_exist, dest->iistate,
- index_slot);
+ if (kind == CHANGE_DELETE)
+ apply_concurrent_delete(rel, tup_exist);
+ else
+ {
+ /* UPDATE */
+ if (!check_range || tup == tup_key ||
+ is_tuple_in_block_range(tup, ctx->first_block,
+ range_end))
+ /* The new tuple is in the same range. */
+ apply_concurrent_update(rel, tup, tup_exist,
+ ctx->iistate, index_slot);
+ else
+
+ /*
+ * The new key is in the other range, so only delete
+ * it from the current one. The new version should be
+ * visible to the snapshot that we'll use to copy the
+ * other block.
+ */
+ apply_concurrent_delete(rel, tup_exist);
+ }
+ }
else
- apply_concurrent_delete(rel, tup_exist);
-
+ {
+ /*
+ * The change belongs to another range, so we don't need to
+ * bother with the old tuple: the snapshot used for the other
+ * range won't see it, so it won't be copied. However, the new
+ * tuple still may need to go to the range we are checking. In
+ * that case, simply insert it there.
+ */
+ if (kind == CHANGE_UPDATE_NEW && tup != tup_key &&
+ is_tuple_in_block_range(tup, ctx->first_block,
+ range_end))
+ apply_concurrent_insert(rel, tup, ctx->iistate,
+ index_slot);
+ }
if (tup_old != NULL)
{
pfree(tup_old);
@@ -2940,6 +3076,33 @@ apply_concurrent_delete(Relation rel, HeapTuple tup_target)
pgstat_progress_incr_param(PROGRESS_REPACK_HEAP_TUPLES_DELETED, 1);
}
+/*
+ * Check if tuple originates from given range of blocks that have already been
+ * copied.
+ */
+static bool
+is_tuple_in_block_range(HeapTuple tup, BlockNumber start, BlockNumber end)
+{
+ BlockNumber blknum;
+
+ Assert(BlockNumberIsValid(start) && BlockNumberIsValid(end));
+
+ blknum = ItemPointerGetBlockNumber(&tup->t_self);
+ Assert(BlockNumberIsValid(blknum));
+
+ if (start < end)
+ {
+ return blknum >= start && blknum < end;
+ }
+ else
+ {
+ /* Has the scan position wrapped around? */
+ Assert(start > end);
+
+ return blknum >= start || blknum < end;
+ }
+}
+
/*
* Find the tuple to be updated or deleted.
*
@@ -2949,10 +3112,10 @@ apply_concurrent_delete(Relation rel, HeapTuple tup_target)
* it when he no longer needs the tuple returned.
*/
static HeapTuple
-find_target_tuple(Relation rel, ChangeDest *dest, HeapTuple tup_key,
- TupleTableSlot *ident_slot)
+find_target_tuple(Relation rel, ConcurrentChangeContext *ctx,
+ HeapTuple tup_key, TupleTableSlot *ident_slot)
{
- Relation ident_index = dest->ident_index;
+ Relation ident_index = ctx->ident_index;
IndexScanDesc scan;
Form_pg_index ident_form;
int2vector *ident_indkey;
@@ -2960,14 +3123,14 @@ find_target_tuple(Relation rel, ChangeDest *dest, HeapTuple tup_key,
/* XXX no instrumentation for now */
scan = index_beginscan(rel, ident_index, GetActiveSnapshot(),
- NULL, dest->ident_key_nentries, 0);
+ NULL, ctx->ident_key_nentries, 0);
/*
* Scan key is passed by caller, so it does not have to be constructed
* multiple times. Key entries have all fields initialized, except for
* sk_argument.
*/
- index_rescan(scan, dest->ident_key, dest->ident_key_nentries, NULL, 0);
+ index_rescan(scan, ctx->ident_key, ctx->ident_key_nentries, NULL, 0);
/* Info needed to retrieve key values from heap tuple. */
ident_form = ident_index->rd_index;
@@ -3002,15 +3165,22 @@ find_target_tuple(Relation rel, ChangeDest *dest, HeapTuple tup_key,
}
/*
- * Decode and apply concurrent changes, up to (and including) the record whose
- * LSN is 'end_of_wal'.
+ * Get concurrent changes, up to (and including) the record whose LSN is
+ * 'end_of_wal', from the decoding worker. If 'range_end' is a valid block
+ * number, the changes should only be applied to blocks greater than or equal
+ * to ctx->first_block and lower than range_end.
+ *
+ * If 'request_snapshot' is true, the snapshot built at LSN following the last
+ * data change needs to be exported too.
*/
-static void
-process_concurrent_changes(XLogRecPtr end_of_wal, ChangeDest *dest, bool done)
+extern void
+repack_get_concurrent_changes(ConcurrentChangeContext *ctx,
+ XLogRecPtr end_of_wal,
+ BlockNumber range_end,
+ bool request_snapshot, bool done)
{
DecodingWorkerShared *shared;
char fname[MAXPGPATH];
- BufFile *file;
pgstat_progress_update_param(PROGRESS_REPACK_PHASE,
PROGRESS_REPACK_PHASE_CATCH_UP);
@@ -3019,6 +3189,8 @@ process_concurrent_changes(XLogRecPtr end_of_wal, ChangeDest *dest, bool done)
shared = (DecodingWorkerShared *) dsm_segment_address(decoding_worker->seg);
SpinLockAcquire(&shared->mutex);
shared->lsn_upto = end_of_wal;
+ Assert(!shared->snapshot_requested);
+ shared->snapshot_requested = request_snapshot;
shared->done = done;
SpinLockRelease(&shared->mutex);
@@ -3030,32 +3202,49 @@ process_concurrent_changes(XLogRecPtr end_of_wal, ChangeDest *dest, bool done)
ConditionVariablePrepareToSleep(&shared->cv);
for (;;)
{
- bool valid;
+ int response;
SpinLockAcquire(&shared->mutex);
- valid = shared->sfs_valid;
+ response = shared->response;
SpinLockRelease(&shared->mutex);
- if (valid)
+ if (response & WORKER_RESPONSE_CHANGES)
break;
ConditionVariableSleep(&shared->cv, WAIT_EVENT_REPACK_WORKER_EXPORT);
}
ConditionVariableCancelSleep();
- /* Open the file. */
- DecodingWorkerFileName(fname, shared->relid, shared->last_exported);
- file = BufFileOpenFileSet(&shared->sfs.fs, fname, O_RDONLY, false);
- apply_concurrent_changes(file, dest);
+ /*
+ * Remember the file name so we can apply the changes when appropriate.
+ * One particular reason to postpone the replay is that indexes haven't
+ * been built yet on the new heap.
+ */
+ DecodingWorkerFileName(fname, shared->relid,
+ shared->last_exported_changes,
+ false);
+ repack_add_block_range(ctx, range_end, fname);
/* No file is exported until the worker exports the next one. */
SpinLockAcquire(&shared->mutex);
- shared->sfs_valid = false;
+ shared->response &= ~WORKER_RESPONSE_CHANGES;
+ Assert(XLogRecPtrIsInvalid(shared->lsn_upto));
SpinLockRelease(&shared->mutex);
+}
- BufFileClose(file);
+static void
+repack_add_block_range(ConcurrentChangeContext *ctx, BlockNumber end,
+ char *fname)
+{
+ RepackApplyRange *range;
+
+ range = palloc_object(RepackApplyRange);
+ range->end = end;
+ range->fname = pstrdup(fname);
+ ctx->block_ranges = lappend(ctx->block_ranges, range);
}
+
/*
* Initialize IndexInsertState for index specified by ident_index_id.
*
@@ -3198,7 +3387,8 @@ static void
rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap,
Relation cl_index,
TransactionId frozenXid,
- MultiXactId cutoffMulti)
+ MultiXactId cutoffMulti,
+ ConcurrentChangeContext *ctx)
{
LOCKMODE lockmode_old PG_USED_FOR_ASSERTS_ONLY;
List *ind_oids_new;
@@ -3217,7 +3407,6 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap,
Relation *ind_refs,
*ind_refs_p;
int nind;
- ChangeDest chgdst;
/* Like in cluster_rel(). */
lockmode_old = ShareUpdateExclusiveLock;
@@ -3274,11 +3463,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap,
(errmsg("identity index missing on the new relation")));
/* Gather information to apply concurrent changes. */
- chgdst.rel = NewHeap;
- chgdst.iistate = get_index_insert_state(NewHeap, ident_idx_new,
- &chgdst.ident_index);
- chgdst.ident_key = build_identity_key(ident_idx_new, OldHeap,
- &chgdst.ident_key_nentries);
+ ctx->rel = NewHeap;
+ ctx->iistate = get_index_insert_state(NewHeap, ident_idx_new,
+ &ctx->ident_index);
+ ctx->ident_key = build_identity_key(ident_idx_new, OldHeap,
+ &ctx->ident_key_nentries);
+
+ /*
+ * Replay the concurrent data changes gathered during heap copying. This
+ * had to wait until after the index build because the identity index is
+ * needed to apply UPDATE and DELETE changes.
+ */
+ apply_concurrent_changes(ctx);
/*
* During testing, wait for another backend to perform concurrent data
@@ -3296,11 +3492,13 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap,
end_of_wal = GetFlushRecPtr(NULL);
/*
- * Apply concurrent changes first time, to minimize the time we need to
- * hold AccessExclusiveLock. (Quite some amount of WAL could have been
+ * Decode and apply concurrent changes again, to minimize the time we need
+ * to hold AccessExclusiveLock. (Quite some amount of WAL could have been
* written during the data copying and index creation.)
*/
- process_concurrent_changes(end_of_wal, &chgdst, false);
+ repack_get_concurrent_changes(ctx, end_of_wal, InvalidBlockNumber, false,
+ false);
+ apply_concurrent_changes(ctx);
/*
* Acquire AccessExclusiveLock on the table, its TOAST relation (if there
@@ -3397,10 +3595,13 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap,
end_of_wal = GetFlushRecPtr(NULL);
/*
- * Apply the concurrent changes again. Indicate that the decoding worker
- * won't be needed anymore.
+ * Decode and apply the concurrent changes again. Indicate that the
+ * decoding worker won't be needed anymore.
*/
- process_concurrent_changes(end_of_wal, &chgdst, true);
+ repack_get_concurrent_changes(ctx, end_of_wal, InvalidBlockNumber, false,
+ true);
+ apply_concurrent_changes(ctx);
+
/* Remember info about rel before closing OldHeap */
relpersistence = OldHeap->rd_rel->relpersistence;
@@ -3451,8 +3652,8 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap,
table_close(NewHeap, NoLock);
/* Cleanup what we don't need anymore. (And close the identity index.) */
- pfree(chgdst.ident_key);
- free_index_insert_state(chgdst.iistate);
+ pfree(ctx->ident_key);
+ free_index_insert_state(ctx->iistate);
/*
* Swap the relations and their TOAST relations and TOAST indexes. This
@@ -3495,6 +3696,23 @@ build_new_indexes(Relation NewHeap, Relation OldHeap, List *OldIndexes)
char *newName;
Relation ind;
+ /*
+ * Try to reduce the impact on VACUUM.
+ *
+ * The individual builds might still be a problem, but that's a
+ * separate issue.
+ *
+ * TODO Can we somehow use the fact that the new heap is not yet
+ * visible to other transaction, and thus cannot be vacuumed? Perhaps
+ * by preventing snapshots from setting MyProc->xmin temporarily. (All
+ * the snapshots that might have participated in the build, including
+ * the catalog snapshots, must not be used for other tables of
+ * course.)
+ */
+ PopActiveSnapshot();
+ InvalidateCatalogSnapshot();
+ PushActiveSnapshot(GetTransactionSnapshot());
+
ind_oid = lfirst_oid(lc);
ind = index_open(ind_oid, ShareUpdateExclusiveLock);
@@ -3534,11 +3752,15 @@ start_decoding_worker(Oid relid)
BUFFERALIGN(REPACK_ERROR_QUEUE_SIZE);
seg = dsm_create(size, 0);
shared = (DecodingWorkerShared *) dsm_segment_address(seg);
+ shared->initialized = false;
shared->lsn_upto = InvalidXLogRecPtr;
shared->done = false;
+ /* Snapshot is the first thing we need from the worker. */
+ shared->snapshot_requested = true;
+ shared->response = 0;
SharedFileSetInit(&shared->sfs, seg);
- shared->sfs_valid = false;
- shared->last_exported = -1;
+ shared->last_exported_changes = -1;
+ shared->last_exported_snapshot = -1;
SpinLockInit(&shared->mutex);
shared->dbid = MyDatabaseId;
@@ -3747,7 +3969,10 @@ repack_worker_internal(dsm_segment *seg)
*/
SpinLockAcquire(&shared->mutex);
Assert(XLogRecPtrIsInvalid(shared->lsn_upto));
- Assert(!shared->sfs_valid);
+ Assert(shared->response == 0);
+ /* Initially we're expected to provide a snapshot and only that. */
+ Assert(shared->snapshot_requested &&
+ XLogRecPtrIsInvalid(shared->lsn_upto));
sfs = &shared->sfs;
SpinLockRelease(&shared->mutex);
@@ -3765,8 +3990,23 @@ repack_worker_internal(dsm_segment *seg)
ConditionVariableSignal(&shared->cv);
/* Build the initial snapshot and export it. */
- snapshot = SnapBuildInitialSnapshotForRepack(decoding_ctx->snapshot_builder);
- export_initial_snapshot(snapshot, shared);
+ snapshot = SnapBuildSnapshotForRepack(decoding_ctx->snapshot_builder);
+ export_snapshot(snapshot, shared);
+
+ /*
+ * Adjust the replication slot's xmin so that VACUUM can do more work.
+ */
+ LogicalIncreaseXminForSlot(InvalidXLogRecPtr, snapshot->xmin, false);
+ FreeSnapshot(snapshot);
+
+ /* Tell the backend that the file is available. */
+ SpinLockAcquire(&shared->mutex);
+ Assert(shared->snapshot_requested);
+ shared->snapshot_requested = false;
+ shared->response |= WORKER_RESPONSE_SNAPSHOT;
+ shared->last_exported_snapshot++;
+ SpinLockRelease(&shared->mutex);
+ ConditionVariableSignal(&shared->cv);
/*
* Only historic snapshots should be used now. Do not let us restrict the
@@ -3786,7 +4026,7 @@ repack_worker_internal(dsm_segment *seg)
* Make snapshot available to the backend that launched the decoding worker.
*/
static void
-export_initial_snapshot(Snapshot snapshot, DecodingWorkerShared *shared)
+export_snapshot(Snapshot snapshot, DecodingWorkerShared *shared)
{
char fname[MAXPGPATH];
BufFile *file;
@@ -3796,29 +4036,23 @@ export_initial_snapshot(Snapshot snapshot, DecodingWorkerShared *shared)
snap_size = EstimateSnapshotSpace(snapshot);
snap_space = (char *) palloc(snap_size);
SerializeSnapshot(snapshot, snap_space);
- FreeSnapshot(snapshot);
- DecodingWorkerFileName(fname, shared->relid, shared->last_exported + 1);
+ DecodingWorkerFileName(fname, shared->relid,
+ shared->last_exported_snapshot + 1,
+ true);
file = BufFileCreateFileSet(&shared->sfs.fs, fname);
/* To make restoration easier, write the snapshot size first. */
BufFileWrite(file, &snap_size, sizeof(snap_size));
BufFileWrite(file, snap_space, snap_size);
pfree(snap_space);
BufFileClose(file);
-
- /* Tell the backend that the file is available. */
- SpinLockAcquire(&shared->mutex);
- shared->sfs_valid = true;
- shared->last_exported++;
- SpinLockRelease(&shared->mutex);
- ConditionVariableSignal(&shared->cv);
}
/*
- * Get the initial snapshot from the decoding worker.
+ * Get snapshot from the decoding worker.
*/
-static Snapshot
-get_initial_snapshot(DecodingWorker *worker)
+extern Snapshot
+repack_get_snapshot(ConcurrentChangeContext *ctx)
{
DecodingWorkerShared *shared;
char fname[MAXPGPATH];
@@ -3826,24 +4060,26 @@ get_initial_snapshot(DecodingWorker *worker)
Size snap_size;
char *snap_space;
Snapshot snapshot;
+ DecodingWorker *worker = ctx->worker;
shared = (DecodingWorkerShared *) dsm_segment_address(worker->seg);
/*
- * The worker needs to initialize the logical decoding, which usually
- * takes some time. Therefore it makes sense to prepare for the sleep
- * first.
+ * For the first snapshot request, the worker needs to initialize the
+ * logical decoding, which usually takes some time. Therefore it makes
+ * sense to prepare for the sleep first. Does it make sense to skip the
+ * preparation on the next requests?
*/
ConditionVariablePrepareToSleep(&shared->cv);
for (;;)
{
- bool valid;
+ int response;
SpinLockAcquire(&shared->mutex);
- valid = shared->sfs_valid;
+ response = shared->response;
SpinLockRelease(&shared->mutex);
- if (valid)
+ if (response & WORKER_RESPONSE_SNAPSHOT)
break;
ConditionVariableSleep(&shared->cv, WAIT_EVENT_REPACK_WORKER_EXPORT);
@@ -3851,7 +4087,9 @@ get_initial_snapshot(DecodingWorker *worker)
ConditionVariableCancelSleep();
/* Read the snapshot from a file. */
- DecodingWorkerFileName(fname, shared->relid, shared->last_exported);
+ DecodingWorkerFileName(fname, shared->relid,
+ shared->last_exported_snapshot,
+ true);
file = BufFileOpenFileSet(&shared->sfs.fs, fname, O_RDONLY, false);
BufFileReadExact(file, &snap_size, sizeof(snap_size));
snap_space = (char *) palloc(snap_size);
@@ -3859,7 +4097,8 @@ get_initial_snapshot(DecodingWorker *worker)
BufFileClose(file);
SpinLockAcquire(&shared->mutex);
- shared->sfs_valid = false;
+ shared->response &= ~WORKER_RESPONSE_SNAPSHOT;
+ Assert(!shared->snapshot_requested);
SpinLockRelease(&shared->mutex);
/* Restore it. */
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index a956892f42f..c8bc85d8bcc 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -1003,6 +1003,7 @@ DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
xl_heap_insert *xlrec;
ReorderBufferChange *change;
RelFileLocator target_locator;
+ BlockNumber blknum;
xlrec = (xl_heap_insert *) XLogRecGetData(r);
@@ -1014,7 +1015,7 @@ DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
return;
/* only interested in our database */
- XLogRecGetBlockTag(r, 0, &target_locator, NULL, NULL);
+ XLogRecGetBlockTag(r, 0, &target_locator, NULL, &blknum);
if (target_locator.dbOid != ctx->slot->data.database)
return;
@@ -1039,6 +1040,15 @@ DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
DecodeXLogTuple(tupledata, datalen, change->data.tp.newtuple);
+ /*
+ * REPACK (CONCURRENTLY) needs block number to check if the corresponding
+ * part of the table was already copied.
+ */
+ if (OidIsValid(repacked_rel_locator.relNumber))
+ /* offnum is not really needed, but let's set valid pointer. */
+ ItemPointerSet(&change->data.tp.newtuple->t_self, blknum,
+ xlrec->offnum);
+
change->data.tp.clear_toast_afterwards = true;
ReorderBufferQueueChange(ctx->reorder, XLogRecGetXid(r), buf->origptr,
@@ -1060,11 +1070,12 @@ DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
ReorderBufferChange *change;
char *data;
RelFileLocator target_locator;
+ BlockNumber new_blknum;
xlrec = (xl_heap_update *) XLogRecGetData(r);
/* only interested in our database */
- XLogRecGetBlockTag(r, 0, &target_locator, NULL, NULL);
+ XLogRecGetBlockTag(r, 0, &target_locator, NULL, &new_blknum);
if (target_locator.dbOid != ctx->slot->data.database)
return;
@@ -1090,12 +1101,27 @@ DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
ReorderBufferAllocTupleBuf(ctx->reorder, tuplelen);
DecodeXLogTuple(data, datalen, change->data.tp.newtuple);
+
+ /*
+ * REPACK (CONCURRENTLY) needs block number to check if the
+ * corresponding part of the table was already copied.
+ */
+ if (OidIsValid(repacked_rel_locator.relNumber))
+ /* offnum is not really needed, but let's set valid pointer. */
+ ItemPointerSet(&change->data.tp.newtuple->t_self,
+ new_blknum, xlrec->new_offnum);
}
if (xlrec->flags & XLH_UPDATE_CONTAINS_OLD)
{
Size datalen;
Size tuplelen;
+ BlockNumber old_blknum;
+
+ if (XLogRecHasBlockRef(r, 1))
+ XLogRecGetBlockTag(r, 1, NULL, NULL, &old_blknum);
+ else
+ XLogRecGetBlockTag(r, 0, NULL, NULL, &old_blknum);
/* caution, remaining data in record is not aligned */
data = XLogRecGetData(r) + SizeOfHeapUpdate;
@@ -1106,6 +1132,11 @@ DecodeUpdate(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
ReorderBufferAllocTupleBuf(ctx->reorder, tuplelen);
DecodeXLogTuple(data, datalen, change->data.tp.oldtuple);
+ /* See above. */
+ if (OidIsValid(repacked_rel_locator.relNumber))
+ ItemPointerSet(&change->data.tp.oldtuple->t_self,
+ old_blknum, xlrec->old_offnum);
+
}
change->data.tp.clear_toast_afterwards = true;
@@ -1126,11 +1157,12 @@ DecodeDelete(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
xl_heap_delete *xlrec;
ReorderBufferChange *change;
RelFileLocator target_locator;
+ BlockNumber blknum;
xlrec = (xl_heap_delete *) XLogRecGetData(r);
/* only interested in our database */
- XLogRecGetBlockTag(r, 0, &target_locator, NULL, NULL);
+ XLogRecGetBlockTag(r, 0, &target_locator, NULL, &blknum);
if (target_locator.dbOid != ctx->slot->data.database)
return;
@@ -1162,6 +1194,15 @@ DecodeDelete(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
DecodeXLogTuple((char *) xlrec + SizeOfHeapDelete,
datalen, change->data.tp.oldtuple);
+
+ /*
+ * REPACK (CONCURRENTLY) needs block number to check if the
+ * corresponding part of the table was already copied.
+ */
+ if (OidIsValid(repacked_rel_locator.relNumber))
+ /* offnum is not really needed, but let's set valid pointer. */
+ ItemPointerSet(&change->data.tp.oldtuple->t_self, blknum,
+ xlrec->offnum);
}
change->data.tp.clear_toast_afterwards = true;
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index b3fd7fec392..1e445704a1b 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -1670,14 +1670,17 @@ update_progress_txn_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
/*
* Set the required catalog xmin horizon for historic snapshots in the current
- * replication slot.
+ * replication slot if catalog is TRUE, or xmin if catalog is FALSE.
*
* Note that in the most cases, we won't be able to immediately use the xmin
* to increase the xmin horizon: we need to wait till the client has confirmed
- * receiving current_lsn with LogicalConfirmReceivedLocation().
+ * receiving current_lsn with LogicalConfirmReceivedLocation(). However,
+ * catalog=FALSE is only allowed for temporary replication slots, so the
+ * horizon is applied immediately.
*/
void
-LogicalIncreaseXminForSlot(XLogRecPtr current_lsn, TransactionId xmin)
+LogicalIncreaseXminForSlot(XLogRecPtr current_lsn, TransactionId xmin,
+ bool catalog)
{
bool updated_xmin = false;
ReplicationSlot *slot;
@@ -1688,6 +1691,27 @@ LogicalIncreaseXminForSlot(XLogRecPtr current_lsn, TransactionId xmin)
Assert(slot != NULL);
SpinLockAcquire(&slot->mutex);
+ if (!catalog)
+ {
+ /*
+ * The non-catalog horizon can only advance in temporary slots, so
+ * update it in the shared memory immediately (w/o requiring prior
+ * saving to disk).
+ */
+ Assert(slot->data.persistency == RS_TEMPORARY);
+
+ /*
+ * The horizon must not go backwards, however it's o.k. to become
+ * invalid.
+ */
+ Assert(!TransactionIdIsValid(slot->effective_xmin) ||
+ !TransactionIdIsValid(xmin) ||
+ TransactionIdFollowsOrEquals(xmin, slot->effective_xmin));
+
+ slot->effective_xmin = xmin;
+ SpinLockRelease(&slot->mutex);
+ return;
+ }
/*
* don't overwrite if we already have a newer xmin. This can happen if we
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index f18c6fb52b5..273f65d6cc8 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -3734,6 +3734,56 @@ ReorderBufferXidHasCatalogChanges(ReorderBuffer *rb, TransactionId xid)
return rbtxn_has_catalog_changes(txn);
}
+/*
+ * Check if a transaction (or its subtransaction) contains a heap change.
+ */
+bool
+ReorderBufferXidHasHeapChanges(ReorderBuffer *rb, TransactionId xid)
+{
+ ReorderBufferTXN *txn;
+ dlist_iter iter;
+
+ txn = ReorderBufferTXNByXid(rb, xid, false, NULL, InvalidXLogRecPtr,
+ false);
+ if (txn == NULL)
+ return false;
+
+ dlist_foreach(iter, &txn->changes)
+ {
+ ReorderBufferChange *change;
+
+ change = dlist_container(ReorderBufferChange, node, iter.cur);
+
+ switch (change->action)
+ {
+ case REORDER_BUFFER_CHANGE_INSERT:
+ case REORDER_BUFFER_CHANGE_UPDATE:
+ case REORDER_BUFFER_CHANGE_DELETE:
+ return true;
+ default:
+ break;
+ }
+ }
+
+ /* Check subtransactions. */
+
+ /*
+ * TODO Verify that subtransactions must be assigned to the top-level
+ * transactions by now.
+ */
+ dlist_foreach(iter, &txn->subtxns)
+ {
+ ReorderBufferTXN *subtxn;
+
+ subtxn = dlist_container(ReorderBufferTXN, node, iter.cur);
+
+ if (ReorderBufferXidHasHeapChanges(rb, subtxn->xid))
+ return true;
+ }
+
+ return false;
+}
+
/*
* ReorderBufferXidHasBaseSnapshot
* Have we already set the base snapshot for the given txn/subtxn?
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 7643dfe31bb..4bc6cd22496 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -128,6 +128,7 @@
#include "access/heapam_xlog.h"
#include "access/transam.h"
#include "access/xact.h"
+#include "commands/cluster.h"
#include "common/file_utils.h"
#include "miscadmin.h"
#include "pgstat.h"
@@ -496,7 +497,7 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
* we do not set MyProc->xmin). XXX Do we yet need to add some restrictions?
*/
Snapshot
-SnapBuildInitialSnapshotForRepack(SnapBuild *builder)
+SnapBuildSnapshotForRepack(SnapBuild *builder)
{
Snapshot snap;
@@ -1035,6 +1036,28 @@ SnapBuildCommitTxn(SnapBuild *builder, XLogRecPtr lsn, TransactionId xid,
}
}
+ /*
+ * Is REPACKED (CONCURRENTLY) is being run by this backend?
+ */
+ else if (OidIsValid(repacked_rel_locator.relNumber))
+ {
+ Assert(builder->building_full_snapshot);
+
+ /*
+ * In this special mode, heap changes of other relations should not be
+ * decoded at all - see heap_decode(). Thus if we find a single heap
+ * change in this transaction (or its subtransaction), we know that
+ * this transaction changes the relation being repacked.
+ */
+ if (ReorderBufferXidHasHeapChanges(builder->reorder, xid))
+
+ /*
+ * Record the commit so we can build snapshots for the relation
+ * being repacked.
+ */
+ needs_timetravel = true;
+ }
+
for (nxact = 0; nxact < nsubxacts; nxact++)
{
TransactionId subxid = subxacts[nxact];
@@ -1240,7 +1263,7 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
xmin = running->oldestRunningXid;
elog(DEBUG3, "xmin: %u, xmax: %u, oldest running: %u, oldest xmin: %u",
builder->xmin, builder->xmax, running->oldestRunningXid, xmin);
- LogicalIncreaseXminForSlot(lsn, xmin);
+ LogicalIncreaseXminForSlot(lsn, xmin, true);
/*
* Also tell the slot where we can restart decoding from. We don't want to
diff --git a/src/backend/replication/pgoutput_repack/pgoutput_repack.c b/src/backend/replication/pgoutput_repack/pgoutput_repack.c
index fb9956d392d..be1c3ec9626 100644
--- a/src/backend/replication/pgoutput_repack/pgoutput_repack.c
+++ b/src/backend/replication/pgoutput_repack/pgoutput_repack.c
@@ -195,6 +195,8 @@ store_change(LogicalDecodingContext *ctx, ConcurrentChangeKind kind,
BufFileWrite(dstate->file, &tuple->t_len, sizeof(tuple->t_len));
/* ... and the tuple itself. */
BufFileWrite(dstate->file, tuple->t_data, tuple->t_len);
+ /* CTID is needed as well, to check block ranges. */
+ BufFileWrite(dstate->file, &tuple->t_self, sizeof(tuple->t_self));
/* Free the flat copy if created above. */
if (flattened)
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index 3b9d8349078..a82d284c44c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2415,6 +2415,16 @@
boot_val => 'true',
},
+# TODO Tune boot_val, 1024 is probably too low.
+{ name => 'repack_snapshot_after', type => 'int', context => 'PGC_USERSET', group => 'DEVELOPER_OPTIONS',
+ short_desc => 'Number of pages after which REPACK (CONCURRENTLY) builds a new snapshot.',
+ flags => 'GUC_UNIT_BLOCKS | GUC_NOT_IN_SAMPLE',
+ variable => 'repack_blocks_per_snapshot',
+ boot_val => '1024',
+ min => '1',
+ max => 'INT_MAX',
+}
+
{ name => 'reserved_connections', type => 'int', context => 'PGC_POSTMASTER', group => 'CONN_AUTH_SETTINGS',
short_desc => 'Sets the number of connection slots reserved for roles with privileges of pg_use_reserved_connections.',
variable => 'ReservedConnections',
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index f87b558c2c6..07f7cfdd6cc 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -42,6 +42,7 @@
#include "catalog/namespace.h"
#include "catalog/storage.h"
#include "commands/async.h"
+#include "commands/cluster.h"
#include "commands/extension.h"
#include "commands/event_trigger.h"
#include "commands/tablespace.h"
diff --git a/src/include/access/tableam.h b/src/include/access/tableam.h
index 321c00682ec..6fe3fc760bc 100644
--- a/src/include/access/tableam.h
+++ b/src/include/access/tableam.h
@@ -629,12 +629,12 @@ typedef struct TableAmRoutine
Relation OldIndex,
bool use_sort,
TransactionId OldestXmin,
- Snapshot snapshot,
TransactionId *xid_cutoff,
MultiXactId *multi_cutoff,
double *num_tuples,
double *tups_vacuumed,
- double *tups_recently_dead);
+ double *tups_recently_dead,
+ void *tableam_data);
/*
* React to VACUUM command on the relation. The VACUUM can be triggered by
@@ -1647,8 +1647,6 @@ table_relation_copy_data(Relation rel, const RelFileLocator *newrlocator)
* not needed for the relation's AM
* - *xid_cutoff - ditto
* - *multi_cutoff - ditto
- * - snapshot - if != NULL, ignore data changes done by transactions that this
- * (MVCC) snapshot considers still in-progress or in the future.
*
* Output parameters:
* - *xid_cutoff - rel's new relfrozenxid value, may be invalid
@@ -1661,19 +1659,19 @@ table_relation_copy_for_cluster(Relation OldTable, Relation NewTable,
Relation OldIndex,
bool use_sort,
TransactionId OldestXmin,
- Snapshot snapshot,
TransactionId *xid_cutoff,
MultiXactId *multi_cutoff,
double *num_tuples,
double *tups_vacuumed,
- double *tups_recently_dead)
+ double *tups_recently_dead,
+ void *tableam_data)
{
OldTable->rd_tableam->relation_copy_for_cluster(OldTable, NewTable, OldIndex,
use_sort, OldestXmin,
- snapshot,
xid_cutoff, multi_cutoff,
num_tuples, tups_vacuumed,
- tups_recently_dead);
+ tups_recently_dead,
+ tableam_data);
}
/*
diff --git a/src/include/commands/cluster.h b/src/include/commands/cluster.h
index 0ac70ec30d7..2b61dce92dc 100644
--- a/src/include/commands/cluster.h
+++ b/src/include/commands/cluster.h
@@ -16,10 +16,12 @@
#include "nodes/execnodes.h"
#include "nodes/parsenodes.h"
#include "parser/parse_node.h"
+#include "postmaster/bgworker.h"
#include "replication/logical.h"
#include "storage/buffile.h"
#include "storage/lock.h"
#include "storage/relfilelocator.h"
+#include "storage/shm_mq.h"
#include "utils/relcache.h"
#include "utils/resowner.h"
#include "utils/tuplestore.h"
@@ -47,6 +49,63 @@ typedef struct ClusterParams
extern RelFileLocator repacked_rel_locator;
extern RelFileLocator repacked_rel_toast_locator;
+extern PGDLLIMPORT int repack_blocks_per_snapshot;
+
+/*
+ * Everything we need to call ExecInsertIndexTuples().
+ */
+typedef struct IndexInsertState
+{
+ ResultRelInfo *rri;
+ EState *estate;
+} IndexInsertState;
+
+/*
+ * Backend-local information to control the decoding worker.
+ */
+typedef struct DecodingWorker
+{
+ /* The worker. */
+ BackgroundWorkerHandle *handle;
+
+ /* DecodingWorkerShared is in this segment. */
+ dsm_segment *seg;
+
+ /* Handle of the error queue. */
+ shm_mq_handle *error_mqh;
+} DecodingWorker;
+
+/*
+ * Information needed to handle concurrent data changes.
+ */
+typedef struct ConcurrentChangeContext
+{
+ /* The relation the changes are applied to. */
+ Relation rel;
+
+ /*
+ * Background worker performing logical decoding of concurrent data
+ * changes.
+ */
+ DecodingWorker *worker;
+
+ /*
+ * The following is needed to find the existing tuple if the change is
+ * UPDATE or DELETE. 'ident_key' should have all the fields except for
+ * 'sk_argument' initialized.
+ */
+ Relation ident_index;
+ ScanKey ident_key;
+ int ident_key_nentries;
+
+ /* Needed to update indexes of rel_dst. */
+ IndexInsertState *iistate;
+
+ /* The first block of the scan used to copy the heap. */
+ BlockNumber first_block;
+ /* List of RepackApplyRange objects. */
+ List *block_ranges;
+} ConcurrentChangeContext;
/*
* Stored as a single byte in the output file.
@@ -102,6 +161,12 @@ extern void finish_heap_swap(Oid OIDOldHeap, Oid OIDNewHeap,
TransactionId frozenXid,
MultiXactId cutoffMulti,
char newrelpersistence);
+extern void repack_get_concurrent_changes(struct ConcurrentChangeContext *ctx,
+ XLogRecPtr end_of_wal,
+ BlockNumber range_end,
+ bool request_snapshot,
+ bool done);
+extern Snapshot repack_get_snapshot(struct ConcurrentChangeContext *ctx);
extern void RepackWorkerMain(Datum main_arg);
#endif /* CLUSTER_H */
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index 2e562bee5a9..9924f706f20 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -137,7 +137,7 @@ extern bool DecodingContextReady(LogicalDecodingContext *ctx);
extern void FreeDecodingContext(LogicalDecodingContext *ctx);
extern void LogicalIncreaseXminForSlot(XLogRecPtr current_lsn,
- TransactionId xmin);
+ TransactionId xmin, bool catalog);
extern void LogicalIncreaseRestartDecodingForSlot(XLogRecPtr current_lsn,
XLogRecPtr restart_lsn);
extern void LogicalConfirmReceivedLocation(XLogRecPtr lsn);
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index 3cbe106a3c7..b6b739f29f4 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -763,6 +763,7 @@ extern void ReorderBufferProcessXid(ReorderBuffer *rb, TransactionId xid, XLogRe
extern void ReorderBufferXidSetCatalogChanges(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn);
extern bool ReorderBufferXidHasCatalogChanges(ReorderBuffer *rb, TransactionId xid);
+extern bool ReorderBufferXidHasHeapChanges(ReorderBuffer *rb, TransactionId xid);
extern bool ReorderBufferXidHasBaseSnapshot(ReorderBuffer *rb, TransactionId xid);
extern bool ReorderBufferRememberPrepareInfo(ReorderBuffer *rb, TransactionId xid,
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index 802fc4b0823..d1f9037fcfb 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -73,7 +73,7 @@ extern void FreeSnapshotBuilder(SnapBuild *builder);
extern void SnapBuildSnapDecRefcount(Snapshot snap);
extern Snapshot SnapBuildInitialSnapshot(SnapBuild *builder);
-extern Snapshot SnapBuildInitialSnapshotForRepack(SnapBuild *builder);
+extern Snapshot SnapBuildSnapshotForRepack(SnapBuild *builder);
extern Snapshot SnapBuildMVCCFromHistoric(Snapshot snapshot, bool in_place);
extern const char *SnapBuildExportSnapshot(SnapBuild *builder);
extern void SnapBuildClearExportedSnapshot(void);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 35344910f65..54115135732 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -411,7 +411,6 @@ CatCacheHeader
CatalogId
CatalogIdMapEntry
CatalogIndexState
-ChangeDest
ChangeVarNodes_callback
ChangeVarNodes_context
CheckPoint
@@ -488,6 +487,7 @@ CompressFileHandle
CompressionLocation
CompressorState
ComputeXidHorizonsResult
+ConcurrentChangeContext
ConcurrentChangeKind
ConditionVariable
ConditionVariableMinimallyPadded
@@ -2563,6 +2563,7 @@ ReorderBufferTupleCidKey
ReorderBufferUpdateProgressTxnCB
ReorderTuple
RepOriginId
+RepackApplyRange
RepackCommand
RepackDecodingState
RepackStmt
--
2.47.3
--=-=-=--
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
* [PATCH v56 1/3] Allow logical replication snapshots to be database-specific
@ 2026-04-06 22:07 Álvaro Herrera <[email protected]>
0 siblings, 0 replies; 103+ messages in thread
From: Álvaro Herrera @ 2026-04-06 22:07 UTC (permalink / raw)
By default, the logical decoding assumes access to shared catalogs, so
the snapshot builder needs to consider cluster-wide XIDs during startup.
That in turn means that, if any transaction is already running (and has
XID assigned), the snapshot builder needs to wait for its completion, as
it does not know if that transaction performed catalog changes earlier.
A possible problem with this concept is that if REPACK (CONCURRENTLY) is
running in some database, backends running the same command in other
databases get stuck until the first one has committed. Thus only a
single backend in the cluster can run REPACK (CONCURRENTLY) at any time.
Likewise, REPACK (CONCURRENTLY) can block walsenders starting on behalf
of subscriptions throughout the cluster.
This patch adds a new option to logical replication output plugin, to
declare that it does not use shared catalogs (i.e. catalogs that can be
changed by transactions running in other databases in the cluster). In
that case, no snapshot the backend will use during the decoding needs to
contain information about transactions running in other databases. Thus
the snapshot builder only needs to wait for completion of transactions
in the current database.
Currently we only use this option in the REPACK background worker. It
could possibly be used in the plugin for logical replication too,
however that would need thorough analysis of that plugin.
Bump WAL version number, due to a new field in xl_running_xacts.
Author: Antonin Houska <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Discussion: https://postgr.es/m/90475.1775218118@localhost
---
contrib/pg_visibility/pg_visibility.c | 4 +-
doc/src/sgml/logicaldecoding.sgml | 4 ++
src/backend/access/index/genam.c | 8 +++
src/backend/access/rmgrdesc/standbydesc.c | 2 +
src/backend/access/transam/xlog.c | 2 +-
src/backend/access/transam/xlogfuncs.c | 2 +-
src/backend/postmaster/bgwriter.c | 2 +-
src/backend/replication/logical/decode.c | 17 +++++-
src/backend/replication/logical/logical.c | 3 +
src/backend/replication/logical/snapbuild.c | 63 ++++++++++++++++++++-
src/backend/replication/pgrepack/pgrepack.c | 7 +++
src/backend/replication/slot.c | 2 +-
src/backend/storage/ipc/procarray.c | 23 +++++++-
src/backend/storage/ipc/standby.c | 24 +++++++-
src/include/access/genam.h | 1 +
src/include/access/xlog_internal.h | 2 +-
src/include/miscadmin.h | 9 +++
src/include/replication/output_plugin.h | 1 +
src/include/replication/snapbuild.h | 3 +-
src/include/storage/procarray.h | 2 +-
src/include/storage/standby.h | 3 +-
src/include/storage/standbydefs.h | 1 +
22 files changed, 167 insertions(+), 18 deletions(-)
diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index dfab0b64cf5..d564bd2a00c 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -621,7 +621,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
else if (rel == NULL || rel->rd_rel->relisshared)
{
/* Shared relation: take into account all running xids */
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestRunningXid;
@@ -632,7 +632,7 @@ GetStrictOldestNonRemovableTransactionId(Relation rel)
* Normal relation: take into account xids running within the current
* database
*/
- runningTransactions = GetRunningTransactionData();
+ runningTransactions = GetRunningTransactionData(InvalidOid);
LWLockRelease(ProcArrayLock);
LWLockRelease(XidGenLock);
return runningTransactions->oldestDatabaseRunningXid;
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 6dc49108997..9b1d68d0de6 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -959,6 +959,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
</programlisting>
<literal>output_type</literal> has to either be set to
@@ -969,6 +970,9 @@ typedef struct OutputPluginOptions
also be called for changes made by heap rewrites during certain DDL
operations. These are of interest to plugins that handle DDL
replication, but they require special handling.
+ <literal>need_shared_catalogs</literal> can be set to false if you are
+ certain the plugin functions do not access shared system catalogs.
+ Doing so can speed up creation of replication slots that use this plugin.
</para>
<para>
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 1408989c568..97d44b84622 100644
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -394,6 +394,14 @@ systable_beginscan(Relation heapRelation,
SysScanDesc sysscan;
Relation irel;
+ /*
+ * If this backend promised that it won't access shared catalogs during
+ * logical decoding, this it the right place to verify.
+ */
+ Assert(!HistoricSnapshotActive() ||
+ accessSharedCatalogsInDecoding ||
+ !heapRelation->rd_rel->relisshared);
+
if (indexOK &&
!IgnoreSystemIndexes &&
!ReindexIsProcessingIndex(indexId))
diff --git a/src/backend/access/rmgrdesc/standbydesc.c b/src/backend/access/rmgrdesc/standbydesc.c
index 0a291354ae2..685d1bdb024 100644
--- a/src/backend/access/rmgrdesc/standbydesc.c
+++ b/src/backend/access/rmgrdesc/standbydesc.c
@@ -41,6 +41,8 @@ standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
for (i = 0; i < xlrec->subxcnt; i++)
appendStringInfo(buf, " %u", xlrec->xids[xlrec->xcnt + i]);
}
+
+ appendStringInfo(buf, "; dbid: %u", xlrec->dbid);
}
void
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b82af9a85c0..3f08a832ca6 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7735,7 +7735,7 @@ CreateCheckPoint(int flags)
* recovery we don't need to write running xact data.
*/
if (!shutdown && XLogStandbyInfoActive())
- LogStandbySnapshot();
+ LogStandbySnapshot(InvalidOid);
START_CRIT_SECTION();
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 65bbaeda59c..0f5979691e6 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -245,7 +245,7 @@ pg_log_standby_snapshot(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
- recptr = LogStandbySnapshot();
+ recptr = LogStandbySnapshot(InvalidOid);
/*
* As a convenience, return the WAL location of the last inserted record
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 1d8947774a9..a30de4262eb 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -289,7 +289,7 @@ BackgroundWriterMain(const void *startup_data, size_t startup_data_len)
if (now >= timeout &&
last_snapshot_lsn <= GetLastImportantRecPtr())
{
- last_snapshot_lsn = LogStandbySnapshot();
+ last_snapshot_lsn = LogStandbySnapshot(InvalidOid);
last_snapshot_ts = now;
}
}
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index c9fea8cad28..38c5a4f5540 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -382,7 +382,16 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
{
xl_running_xacts *running = (xl_running_xacts *) XLogRecGetData(r);
- SnapBuildProcessRunningXacts(builder, buf->origptr, running);
+ /*
+ * Update this decoder's idea of transactions currently
+ * running. In doing so we will determine whether we have
+ * reached consistent status.
+ *
+ * If the output plugin doesn't need access to shared
+ * catalogs, we can ignore transactions in other databases.
+ */
+ SnapBuildProcessRunningXacts(builder, buf->origptr, running,
+ !ctx->options.need_shared_catalogs);
/*
* Abort all transactions that we keep track of, that are
@@ -392,8 +401,12 @@ standby_decode(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
* all running transactions which includes prepared ones,
* while shutdown checkpoints just know that no non-prepared
* transactions are in progress.
+ *
+ * The database-specific records might work here too, but it's
+ * not their purpose.
*/
- ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
+ if (!OidIsValid(running->dbid))
+ ReorderBufferAbortOld(ctx->reorder, running->oldestRunningXid);
}
break;
case XLOG_STANDBY_LOCK:
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index f20d0c542f3..8ceaf64d164 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -285,6 +285,9 @@ StartupDecodingContext(List *output_plugin_options,
ctx->write = do_write;
ctx->update_progress = update_progress;
+ /* Assume shared catalog access. The startup callback can change it. */
+ ctx->options.need_shared_catalogs = true;
+
ctx->output_plugin_options = output_plugin_options;
ctx->fast_forward = fast_forward;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b4269a3b102..ffb4ab2cf2a 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -154,6 +154,14 @@
static ResourceOwner SavedResourceOwnerDuringExport = NULL;
static bool ExportInProgress = false;
+/*
+ * If a backend is going to do logical decoding and the output plugin does
+ * not need to access shared catalogs, setting this variable to false can make
+ * the decoding startup faster. In particular, the backend will not need to
+ * wait for completion of already running transactions in other databases.
+ */
+bool accessSharedCatalogsInDecoding = true;
+
/* ->committed and ->catchange manipulation */
static void SnapBuildPurgeOlderTxn(SnapBuild *builder);
@@ -170,7 +178,8 @@ static inline bool SnapBuildXidHasCatalogChanges(SnapBuild *builder, Transaction
uint32 xinfo);
/* xlog reading helper functions for SnapBuildProcessRunningXacts */
-static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running);
+static bool SnapBuildFindSnapshot(SnapBuild *builder, XLogRecPtr lsn,
+ xl_running_xacts *running);
static void SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff);
/* serialization functions */
@@ -226,6 +235,9 @@ AllocateSnapshotBuilder(ReorderBuffer *reorder,
MemoryContextSwitchTo(oldcontext);
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
return builder;
}
@@ -244,6 +256,9 @@ FreeSnapshotBuilder(SnapBuild *builder)
builder->snapshot = NULL;
}
+ /* The default is that shared catalog are used. */
+ accessSharedCatalogsInDecoding = true;
+
/* other resources are deallocated via memory context reset */
MemoryContextDelete(context);
}
@@ -1136,7 +1151,8 @@ SnapBuildXidHasCatalogChanges(SnapBuild *builder, TransactionId xid,
* anymore.
*/
void
-SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running)
+SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xacts *running,
+ bool db_specific)
{
ReorderBufferTXN *txn;
TransactionId xmin;
@@ -1148,6 +1164,33 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
*/
if (builder->state < SNAPBUILD_CONSISTENT)
{
+ /*
+ * To reduce the potential for unnecessarily waiting for completion of
+ * unrelated transactions, the caller can declare that only
+ * transactions of the current database are relevant at this stage.
+ */
+ if (db_specific)
+ {
+ /*
+ * If we must only keep track of transactions running in the
+ * current database, we need transaction info from exactly that
+ * database.
+ */
+ if (running->dbid != MyDatabaseId)
+ {
+ LogStandbySnapshot(MyDatabaseId);
+
+ return;
+ }
+
+ /*
+ * We'd better be able to check during scan if the plugin does not
+ * lie.
+ */
+ if (accessSharedCatalogsInDecoding)
+ accessSharedCatalogsInDecoding = false;
+ }
+
/* returns false if there's no point in performing cleanup just yet */
if (!SnapBuildFindSnapshot(builder, lsn, running))
return;
@@ -1155,6 +1198,16 @@ SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn, xl_running_xact
else
SnapBuildSerialize(builder, lsn);
+ /*
+ * Database specific transaction info may exist to reach CONSISTENT state
+ * faster, however the code below makes no use of it. Moreover, such
+ * record might cause problems because the following normal (cluster-wide)
+ * record can have lower value of oldestRunningXid. In that case, let's
+ * wait with the cleanup for the next regular cluster-wide record.
+ */
+ if (OidIsValid(running->dbid))
+ return;
+
/*
* Update range of interesting xids based on the running xacts
* information. We don't increase ->xmax using it, because once we are in
@@ -1465,7 +1518,11 @@ SnapBuildWaitSnapshot(xl_running_xacts *running, TransactionId cutoff)
*/
if (!RecoveryInProgress())
{
- LogStandbySnapshot();
+ /*
+ * If the last transaction info was about specific database, so needs
+ * to be the next one - at least until we're in the CONSISTENT state.
+ */
+ LogStandbySnapshot(running->dbid);
}
}
diff --git a/src/backend/replication/pgrepack/pgrepack.c b/src/backend/replication/pgrepack/pgrepack.c
index 457b6518a8e..4da66aa0f44 100644
--- a/src/backend/replication/pgrepack/pgrepack.c
+++ b/src/backend/replication/pgrepack/pgrepack.c
@@ -52,6 +52,13 @@ repack_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
/* Probably unnecessary, as we don't use the SQL interface ... */
opt->output_type = OUTPUT_PLUGIN_BINARY_OUTPUT;
+ /*
+ * REPACK doesn't need access to shared catalogs, so we can speed up the
+ * historic snapshot creation by setting this flag. We'll only have to
+ * wait for transactions in our database.
+ */
+ opt->need_shared_catalogs = false;
+
if (ctx->output_plugin_options != NIL)
{
ereport(ERROR,
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 21a213a0ebf..a1f37e59dbc 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1756,7 +1756,7 @@ ReplicationSlotReserveWal(void)
XLogRecPtr flushptr;
/* make sure we have enough information to start */
- flushptr = LogStandbySnapshot();
+ flushptr = LogStandbySnapshot(InvalidOid);
/* and make sure it's fsynced to disk */
XLogFlush(flushptr);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index f540bb6b23f..9299bcebbda 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -2623,9 +2623,11 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
*
* Note that if any transaction has overflowed its cached subtransactions
* then there is no real need include any subtransactions.
+ *
+ * If 'dbid' is valid, only gather transactions running in that database.
*/
RunningTransactions
-GetRunningTransactionData(void)
+GetRunningTransactionData(Oid dbid)
{
/* result workspace */
static RunningTransactionsData CurrentRunningXactsData;
@@ -2700,6 +2702,18 @@ GetRunningTransactionData(void)
if (!TransactionIdIsValid(xid))
continue;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid))
+ {
+ int pgprocno = arrayP->pgprocnos[index];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->databaseId != dbid)
+ continue;
+ }
+
/*
* Be careful not to exclude any xids before calculating the values of
* oldestRunningXid and suboverflowed, since these are used to clean
@@ -2750,6 +2764,12 @@ GetRunningTransactionData(void)
PGPROC *proc = &allProcs[pgprocno];
int nsubxids;
+ /*
+ * Filter by database OID if requested.
+ */
+ if (OidIsValid(dbid) && proc->databaseId != dbid)
+ continue;
+
/*
* Save subtransaction XIDs. Other backends can't add or remove
* entries while we're holding XidGenLock.
@@ -2783,6 +2803,7 @@ GetRunningTransactionData(void)
* increases if slots do.
*/
+ CurrentRunningXacts->dbid = dbid;
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_status = suboverflowed ? SUBXIDS_IN_SUBTRANS : SUBXIDS_IN_ARRAY;
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index de9092fdf5b..29af7733948 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -1188,6 +1188,14 @@ standby_redo(XLogReaderState *record)
xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
RunningTransactionsData running;
+ /*
+ * Records issued for specific database are not suitable for physical
+ * replication because that affects the whole cluster. In particular,
+ * the list of XID is probably incomplete here.
+ */
+ if (OidIsValid(xlrec->dbid))
+ return;
+
running.xcnt = xlrec->xcnt;
running.subxcnt = xlrec->subxcnt;
running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
@@ -1277,11 +1285,22 @@ standby_redo(XLogReaderState *record)
* as there's no independent knob to just enable logical decoding. For
* details of how this is used, check snapbuild.c's introductory comment.
*
+ * If 'dbid' is valid, only gather transactions running in that
+ * database. snapbuild.c can use such running xacts information for faster
+ * startup, but it still needs normal (cluster-wide) during the actual
+ * decoding - see standby_decode() and SnapBuildProcessRunningXacts() for
+ * details. Other processes (e.g. checkpointer) issue the cluster-wide records
+ * whether logical decoding is active or not.
+ *
+ * Please be careful about using this argument for other purposes. In
+ * particular, physical replication *must* ignore the database-specific
+ * records, exactly because they do not cover the whole cluster - see
+ * standby_redo().
*
* Returns the RecPtr of the last inserted record.
*/
XLogRecPtr
-LogStandbySnapshot(void)
+LogStandbySnapshot(Oid dbid)
{
XLogRecPtr recptr;
RunningTransactions running;
@@ -1314,7 +1333,7 @@ LogStandbySnapshot(void)
* Log details of all in-progress transactions. This should be the last
* record we write, because standby will open up when it sees this.
*/
- running = GetRunningTransactionData();
+ running = GetRunningTransactionData(dbid);
/*
* GetRunningTransactionData() acquired ProcArrayLock, we must release it.
@@ -1358,6 +1377,7 @@ LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
xl_running_xacts xlrec;
XLogRecPtr recptr;
+ xlrec.dbid = CurrRunningXacts->dbid;
xlrec.xcnt = CurrRunningXacts->xcnt;
xlrec.subxcnt = CurrRunningXacts->subxcnt;
xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
diff --git a/src/include/access/genam.h b/src/include/access/genam.h
index b69320a7fc8..de55821e414 100644
--- a/src/include/access/genam.h
+++ b/src/include/access/genam.h
@@ -136,6 +136,7 @@ typedef struct IndexOrderByDistance
bool isnull;
} IndexOrderByDistance;
+
/*
* generalized index_ interface routines (in indexam.c)
*/
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 10c18d39ff8..13ae3ad4fbb 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -32,7 +32,7 @@
/*
* Each page of XLOG file has a header like this:
*/
-#define XLOG_PAGE_MAGIC 0xD11E /* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD11F /* can be used as WAL version indicator */
typedef struct XLogPageHeaderData
{
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 2e10e3c814d..93b7816c09c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -310,6 +310,15 @@ extern void PreventCommandIfReadOnly(const char *cmdname);
extern void PreventCommandIfParallelMode(const char *cmdname);
extern void PreventCommandDuringRecovery(const char *cmdname);
+/* in replication/snapbuild.c */
+
+/*
+ * Keep track of whether logical decoding in this backend promised not to
+ * access shared catalogs, as a safety check. This is checked by genam.c when
+ * a catalog scan takes place to verify that no shared catalogs are accessed.
+ */
+extern bool accessSharedCatalogsInDecoding;
+
/*****************************************************************************
* pdir.h -- *
* POSTGRES directory path definitions. *
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 842fcde67f9..917f3cff232 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -27,6 +27,7 @@ typedef struct OutputPluginOptions
{
OutputPluginOutputType output_type;
bool receive_rewrites;
+ bool need_shared_catalogs;
} OutputPluginOptions;
/*
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index a22a83a2f23..d02530a912a 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -92,7 +92,8 @@ extern void SnapBuildProcessNewCid(SnapBuild *builder, TransactionId xid,
XLogRecPtr lsn,
xl_heap_new_cid *xlrec);
extern void SnapBuildProcessRunningXacts(SnapBuild *builder, XLogRecPtr lsn,
- xl_running_xacts *running);
+ xl_running_xacts *running,
+ bool db_specific);
extern void SnapBuildSerializationPoint(SnapBuild *builder, XLogRecPtr lsn);
extern bool SnapBuildSnapshotExists(XLogRecPtr lsn);
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index d718a5b542f..ec89c448220 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -47,7 +47,7 @@ extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
VirtualTransactionId *sourcevxid);
extern bool ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc);
-extern RunningTransactions GetRunningTransactionData(void);
+extern RunningTransactions GetRunningTransactionData(Oid dbid);
extern bool TransactionIdIsInProgress(TransactionId xid);
extern TransactionId GetOldestNonRemovableTransactionId(Relation rel);
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 6a314c693cd..8715c08e94f 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -126,6 +126,7 @@ typedef enum
typedef struct RunningTransactionsData
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
subxids_array_status subxid_status;
@@ -143,7 +144,7 @@ typedef RunningTransactionsData *RunningTransactions;
extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
extern void LogAccessExclusiveLockPrepare(void);
-extern XLogRecPtr LogStandbySnapshot(void);
+extern XLogRecPtr LogStandbySnapshot(Oid dbid);
extern void LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInitFileInval);
diff --git a/src/include/storage/standbydefs.h b/src/include/storage/standbydefs.h
index 231d251fd51..e75b7078766 100644
--- a/src/include/storage/standbydefs.h
+++ b/src/include/storage/standbydefs.h
@@ -46,6 +46,7 @@ typedef struct xl_standby_locks
*/
typedef struct xl_running_xacts
{
+ Oid dbid; /* only track xacts in this database */
int xcnt; /* # of xact ids in xids[] */
int subxcnt; /* # of subxact ids in xids[] */
bool subxid_overflow; /* snapshot overflowed, subxids missing */
--
2.47.3
--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
filename="v56-0002-Reserve-replication-slots-specifically-for-REPAC.patch"
^ permalink raw reply [nested|flat] 103+ messages in thread
end of thread, other threads:[~2026-04-06 22:07 UTC | newest]
Thread overview: 103+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2022-06-17 01:33 [PATCH v1 2/2] WIP: Fix EEOP_JSON_CONSTRUCTOR and EEOP_JSONEXPR size. Andres Freund <[email protected]>
2025-12-13 18:27 [PATCH 6/6] Use multiple snapshots to copy the data. Antonin Houska <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
2026-04-06 22:07 [PATCH v56 1/3] Allow logical replication snapshots to be database-specific Álvaro Herrera <[email protected]>
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