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[PATCH] Lock upgrade without deadlocks. 75+ messages / 2 participants [nested] [flat]
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH] Lock upgrade without deadlocks. @ 2026-04-17 13:13 Antonin Houska <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Antonin Houska @ 2026-04-17 13:13 UTC (permalink / raw) For REPACK (CONCURRENTLY), it's essential to upgrade ShareUpdateExclusive lock to AccessExclusiveLock for the final stage of table processing. However, we cannot release the earlier before requesting the latter, because if another process ran DDL on the table in between, REPACK would have to cancel its transaction, and waste possibly a lot of work. Without releasing ShareUpdateExclusive lock, the upgrade can cause deadlock, and it's not really deterministic whether REPACK or the other process will get canceled. This patch adds a new field to the LOCK structure which tells which process is trying to upgrade the lock - this field is set right before the upgrade. All processes waiting in the lock queue are then woken up to check the flag. When another process tries to get the lock after that, it checks this field, and if it's set, it checks for deadlocks even if deadlock timeout hasn't expired yet. If the process is already in the lock's queue and sleeping, the lock upgrading process wakes it up so it checks the flag immediately. At the time the upgrading process starts to sleep, all the other process should be aware that they need to check for deadlock during their lock acquisitions, so the upgrading process does not have to check for deadlocks when it gets woken up. Thus it should never receive deadlock error report. --- src/backend/commands/repack.c | 4 +- src/backend/storage/lmgr/lmgr.c | 35 ++++++++--- src/backend/storage/lmgr/lock.c | 107 +++++++++++++++++++++++++++++++- src/backend/storage/lmgr/proc.c | 32 +++++++--- src/include/storage/lmgr.h | 1 + src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 4 +- 7 files changed, 166 insertions(+), 22 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..310b2a65099 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -3055,8 +3055,10 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, /* * Acquire AccessExclusiveLock on the table, its TOAST relation (if there * is one), all its indexes, so that we can swap the files. + * + * TODO The same for indexes and TOAST? */ - LockRelationOid(old_table_oid, AccessExclusiveLock); + LockRelationOidUpgrade(old_table_oid, AccessExclusiveLock); /* * Lock all indexes now, not only the clustering one: all indexes need to diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 2ccf7237fee..0b103485d54 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -58,6 +58,8 @@ typedef struct XactLockTableWaitInfo const ItemPointerData *ctid; } XactLockTableWaitInfo; +static void LockRelationOidCommon(Oid relid, LOCKMODE lockmode, + bool isUpgrade); static void XactLockTableWaitErrorCb(void *arg); /* @@ -105,6 +107,21 @@ SetLocktagRelationOid(LOCKTAG *tag, Oid relid) */ void LockRelationOid(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, false); +} + +/* + * Like above, but upgrade an existing lock. + */ +void +LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode) +{ + LockRelationOidCommon(relid, lockmode, true); +} + +static void +LockRelationOidCommon(Oid relid, LOCKMODE lockmode, bool isUpgrade) { LOCKTAG tag; LOCALLOCK *locallock; @@ -113,7 +130,7 @@ LockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, isUpgrade); /* * Now that we have the lock, check for invalidation messages, so that we @@ -157,7 +174,7 @@ ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode) SetLocktagRelationOid(&tag, relid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -191,7 +208,7 @@ LockRelationId(LockRelId *relid, LOCKMODE lockmode) SET_LOCKTAG_RELATION(tag, relid->dbId, relid->relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -254,7 +271,7 @@ LockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, false, true, &locallock, - false); + false, false); /* * Now that we have the lock, check for invalidation messages; see notes @@ -286,7 +303,7 @@ ConditionalLockRelation(Relation relation, LOCKMODE lockmode) relation->rd_lockInfo.lockRelId.relId); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -591,7 +608,7 @@ ConditionalLockTuple(Relation relation, const ItemPointerData *tid, LOCKMODE loc ItemPointerGetOffsetNumber(tid)); return (LockAcquireExtended(&tag, lockmode, false, true, true, NULL, - logLockFailure) != LOCKACQUIRE_NOT_AVAIL); + logLockFailure, false) != LOCKACQUIRE_NOT_AVAIL); } /* @@ -749,7 +766,7 @@ ConditionalXactLockTableWait(TransactionId xid, bool logLockFailure) SET_LOCKTAG_TRANSACTION(tag, xid); if (LockAcquireExtended(&tag, ShareLock, false, true, true, NULL, - logLockFailure) + logLockFailure, false) == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1043,7 +1060,7 @@ ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; @@ -1123,7 +1140,7 @@ ConditionalLockSharedObject(Oid classid, Oid objid, uint16 objsubid, objsubid); res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock, - false); + false, false); if (res == LOCKACQUIRE_NOT_AVAIL) return false; diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..bcbbf36c091 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -810,7 +810,7 @@ LockAcquire(const LOCKTAG *locktag, bool dontWait) { return LockAcquireExtended(locktag, lockmode, sessionLock, dontWait, - true, NULL, false); + true, NULL, false, false); } /* @@ -829,6 +829,9 @@ LockAcquire(const LOCKTAG *locktag, * * logLockFailure indicates whether to log details when a lock acquisition * fails with dontWait = true. + * + * isUpgrade should be true if the backend already holds this lock in a lower + * mode. */ LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, @@ -837,7 +840,8 @@ LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure) + bool logLockFailure, + bool isUpgrade) { LOCKMETHODID lockmethodid = locktag->locktag_lockmethodid; LockMethod lockMethodTable; @@ -1119,7 +1123,8 @@ LockAcquireExtended(const LOCKTAG *locktag, * case, because JoinWaitQueue() may discover that we can acquire the * lock immediately after all. */ - waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait); + waitResult = JoinWaitQueue(locallock, lockMethodTable, dontWait, + isUpgrade); } if (waitResult == PROC_WAIT_STATUS_ERROR) @@ -1225,8 +1230,85 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!dontWait); PROCLOCK_PRINT("LockAcquire: sleeping on lock", proclock); LOCK_PRINT("LockAcquire: sleeping on lock", lock, lockmode); + + /* + * Lock upgrade can introduce deadlock, therefore enforce special + * behavior of other processes that deal with this lock. In + * particular, any waiter that sees upgradedBy set is expected to + * perform deadlock check as soon as it's woken up. (Since we are + * already in the queue, the deadlock detector has all the information + * it needs.) + */ + if (isUpgrade) + { + dlist_iter iter; + + /* + * There should not be multiple upgrades at the same time. XXX + * ERROR ? + */ + Assert(lock->upgradedBy == NULL); + + lock->upgradedBy = MyProc; + + /* + * Now, before I sleep myself, wake up all the existing waiters + * (except for me), so they check for deadlock. + */ + dclist_foreach(iter, &lock->waitProcs) + { + PGPROC *proc = dlist_container(PGPROC, waitLink, + iter.cur); + + if (proc != MyProc) + SetLatch(&proc->procLatch); + } + } LWLockRelease(partitionLock); + if (!isUpgrade) + { + HASH_SEQ_STATUS status; + LOCALLOCK *llock; + bool check_deadlock = false; + + /* + * Likewise, new waiters should check the isUpgrade flag and + * engage deadlock detector if needed. The lock being acquired + * should already be in the hash. + * + * Note that, to make deadlock detection happen as soon as + * possible (i.e. regardless deadlock timeout), we check the other + * locks too. XXX There might be ways to get into the deadlock + * indirectly, but that needs more analysis. As long as the + * upgrading process skips deadlock detection altogether, the + * worst consequence of missing some lock wait cycle here is that + * the other process will be kicked-off no sooner than after its + * deadlock timeout has elapsed. (Which in turn means that the + * lock upgrade will take longer than expected.) + */ + hash_seq_init(&status, LockMethodLocalHash); + while ((llock = (LOCALLOCK *) hash_seq_search(&status)) != NULL) + { + LOCK *mylock = llock->lock; + + if (mylock && mylock->upgradedBy) + { + check_deadlock = true; + break; + } + } + /* Check for deadlock if needed. */ + if (check_deadlock) + { + DeadLockState deadlock_state; + + deadlock_state = CheckDeadLock(); + if (deadlock_state == DS_HARD_DEADLOCK) + DeadLockReport(); + } + } + waitResult = WaitOnLock(locallock, owner); /* @@ -1245,6 +1327,18 @@ LockAcquireExtended(const LOCKTAG *locktag, DeadLockReport(); /* DeadLockReport() will not return */ } + + /* + * If finishing the lock upgrade, we should not get into a deadlock + * anymore, so let others know that they do not have to care either. + */ + if (isUpgrade) + { + LWLockAcquire(partitionLock, LW_EXCLUSIVE); + Assert(lock->upgradedBy != NULL); + lock->upgradedBy = NULL; + LWLockRelease(partitionLock); + } } else LWLockRelease(partitionLock); @@ -1322,6 +1416,7 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, lock->nGranted = 0; MemSet(lock->requested, 0, sizeof(int) * MAX_LOCKMODES); MemSet(lock->granted, 0, sizeof(int) * MAX_LOCKMODES); + lock->upgradedBy = NULL; LOCK_PRINT("LockAcquire: new", lock, lockmode); } else @@ -1768,6 +1863,12 @@ CleanUpLock(LOCK *lock, PROCLOCK *proclock, elog(PANIC, "proclock table corrupted"); } + /* + * Was this backend upgrading the lock? + */ + if (lock->upgradedBy == MyProc) + lock->upgradedBy = NULL; + if (lock->nRequested == 0) { /* diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..7b31370db70 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -95,7 +95,6 @@ static volatile sig_atomic_t got_deadlock_timeout; static void RemoveProcFromArray(int code, Datum arg); static void ProcKill(int code, Datum arg); static void AuxiliaryProcKill(int code, Datum arg); -static DeadLockState CheckDeadLock(void); /* @@ -1143,7 +1142,8 @@ AuxiliaryPidGetProc(int pid) * NOTES: The process queue is now a priority queue for locking. */ ProcWaitStatus -JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) +JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait, + bool isUpgrade) { LOCKMODE lockmode = locallock->tag.mode; LOCK *lock = locallock->lock; @@ -1230,8 +1230,12 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) /* Must he wait for me? */ if (lockMethodTable->conflictTab[proc->waitLockMode] & myHeldLocks) { - /* Must I wait for him ? */ - if (lockMethodTable->conflictTab[lockmode] & proc->heldLocks) + /* + * Must I wait for him? I don't want a deadlock during lock + * upgrade - other processes should fail on it. + */ + if ((lockMethodTable->conflictTab[lockmode] & proc->heldLocks) && + !isUpgrade) { /* * Yes, so we have a deadlock. Easiest way to clean up @@ -1461,8 +1465,22 @@ ProcSleep(LOCALLOCK *locallock) (void) WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH, 0, PG_WAIT_LOCK | locallock->tag.lock.locktag_type); ResetLatch(MyLatch); - /* check for deadlocks first, as that's probably log-worthy */ - if (got_deadlock_timeout) + /* + * Check for deadlocks first, as that's probably log-worthy. + * + * Do not wait for the timeout if the lock is being upgraded since + * the risk of deadlock is higher now. However, do not check for + * deadlock if the lock is being upgraded by this process - other + * processes should take care. + * + * TODO Possible optimization: if this is the only lock of the + * backend and if it did not have any weaker lock on the table so + * far, it should be safe to skip the deadlock check. However, to + * evaluate the situation, we need to take fast-path locks into + * account. + */ + if ((got_deadlock_timeout || lock->upgradedBy) && + lock->upgradedBy != MyProc) { deadlock_state = CheckDeadLock(); got_deadlock_timeout = false; @@ -1819,7 +1837,7 @@ ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock) * not, just return. If we have a real deadlock, remove ourselves from the * lock's wait queue. */ -static DeadLockState +DeadLockState CheckDeadLock(void) { int i; diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index 2a985ce5e15..eddbe1e8622 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -38,6 +38,7 @@ extern void RelationInitLockInfo(Relation relation); /* Lock a relation */ extern void LockRelationOid(Oid relid, LOCKMODE lockmode); +extern void LockRelationOidUpgrade(Oid relid, LOCKMODE lockmode); extern void LockRelationId(LockRelId *relid, LOCKMODE lockmode); extern bool ConditionalLockRelationOid(Oid relid, LOCKMODE lockmode); extern void UnlockRelationId(LockRelId *relid, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..080b69eddfd 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -131,6 +131,7 @@ typedef const LockMethodData *LockMethod; * nRequested -- total requested locks of all types. * granted -- count of each lock type currently granted on the lock. * nGranted -- total granted locks of all types. + * upgrader -- process that intends to upgrade the lock * * Note: these counts count 1 for each backend. Internally to a backend, * there may be multiple grabs on a particular lock, but this is not reflected @@ -150,6 +151,7 @@ typedef struct LOCK int nRequested; /* total of requested[] array */ int granted[MAX_LOCKMODES]; /* counts of granted locks */ int nGranted; /* total of granted[] array */ + PGPROC *upgradedBy; /* is lock being upgraded by this process? */ } LOCK; #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid) @@ -390,7 +392,8 @@ extern LockAcquireResult LockAcquireExtended(const LOCKTAG *locktag, bool dontWait, bool reportMemoryError, LOCALLOCK **locallockp, - bool logLockFailure); + bool logLockFailure, + bool isUpgrade); extern void AbortStrongLockAcquire(void); extern void MarkLockClear(LOCALLOCK *locallock); extern bool LockRelease(const LOCKTAG *locktag, diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..c4bc3a24044 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -563,10 +563,12 @@ extern bool HaveNFreeProcs(int n, int *nfree); extern void ProcReleaseLocks(bool isCommit); extern ProcWaitStatus JoinWaitQueue(LOCALLOCK *locallock, - LockMethod lockMethodTable, bool dontWait); + LockMethod lockMethodTable, bool dontWait, + bool isUpgrade); extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock); extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); +extern DeadLockState CheckDeadLock(void); extern void CheckDeadLockAlert(void); extern void LockErrorCleanup(void); extern void GetLockHoldersAndWaiters(LOCALLOCK *locallock, -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 75+ messages in thread
* [PATCH v2] Fix DROP PROPERTY GRAPH "unsupported object class" error @ 2026-04-23 09:27 Bertrand Drouvot <[email protected]> 0 siblings, 0 replies; 75+ messages in thread From: Bertrand Drouvot @ 2026-04-23 09:27 UTC (permalink / raw) getObjectTypeDescription() and getObjectIdentityParts() are missing switch cases for PropgraphElementLabelRelationId and PropgraphLabelPropertyRelationId, causing them to hit the default case and error out with "unsupported object class". During DROP PROPERTY GRAPH, this manifests when an event trigger is active, because pg_event_trigger_ddl_commands() calls these functions. The same code paths are also reachable via pg_identify_object() and pg_identify_object_as_address(). This commit adds the missing cases. Test coverage is added in object_address.sql for these two catalog types via the zero-OID test that exercises pg_identify_object() and pg_identify_object_as_address(). A test in event_trigger.sql verifies that DROP PROPERTY GRAPH works correctly when an event trigger is active. Author: Bertrand Drouvot <[email protected]> Reviewed-by: Michael Paquier <[email protected]> Reviewed-by: Ashutosh Bapat <[email protected]> Discussion: https://postgr.es/m/aej1DkLwhyZWmtxJ@bdtpg --- src/backend/catalog/objectaddress.c | 93 ++++++++++++++++++++ src/test/regress/expected/event_trigger.out | 17 ++++ src/test/regress/expected/object_address.out | 4 + src/test/regress/sql/event_trigger.sql | 13 +++ src/test/regress/sql/object_address.sql | 2 + 5 files changed, 129 insertions(+) 62.4% src/backend/catalog/ 25.6% src/test/regress/expected/ 11.8% src/test/regress/sql/ diff --git a/src/backend/catalog/objectaddress.c b/src/backend/catalog/objectaddress.c index c1862809577..e2d6d8f71f6 100644 --- a/src/backend/catalog/objectaddress.c +++ b/src/backend/catalog/objectaddress.c @@ -4901,10 +4901,18 @@ getObjectTypeDescription(const ObjectAddress *object, bool missing_ok) appendStringInfoString(&buffer, "policy"); break; + case PropgraphElementLabelRelationId: + appendStringInfoString(&buffer, "property graph element label"); + break; + case PropgraphElementRelationId: appendStringInfoString(&buffer, "property graph element"); break; + case PropgraphLabelPropertyRelationId: + appendStringInfoString(&buffer, "property graph label property"); + break; + case PropgraphLabelRelationId: appendStringInfoString(&buffer, "property graph label"); break; @@ -6161,6 +6169,49 @@ getObjectIdentityParts(const ObjectAddress *object, break; } + case PropgraphElementLabelRelationId: + { + Relation ellabelDesc; + ScanKeyData skey[1]; + SysScanDesc ellabelscan; + HeapTuple tup; + Form_pg_propgraph_element_label pgelform; + ObjectAddress oa; + + ellabelDesc = table_open(PropgraphElementLabelRelationId, AccessShareLock); + ScanKeyInit(&skey[0], + Anum_pg_propgraph_element_label_oid, + BTEqualStrategyNumber, F_OIDEQ, + ObjectIdGetDatum(object->objectId)); + + ellabelscan = systable_beginscan(ellabelDesc, + PropgraphElementLabelObjectIndexId, + true, NULL, 1, skey); + + tup = systable_getnext(ellabelscan); + if (!HeapTupleIsValid(tup)) + { + if (!missing_ok) + elog(ERROR, "could not find tuple for element label %u", + object->objectId); + + systable_endscan(ellabelscan); + table_close(ellabelDesc, AccessShareLock); + break; + } + + pgelform = (Form_pg_propgraph_element_label) GETSTRUCT(tup); + + ObjectAddressSet(oa, PropgraphElementRelationId, pgelform->pgelelid); + + appendStringInfoString(&buffer, getObjectIdentityParts(&oa, objname, + objargs, false)); + + systable_endscan(ellabelscan); + table_close(ellabelDesc, AccessShareLock); + break; + } + case PropgraphElementRelationId: { HeapTuple tup; @@ -6184,6 +6235,48 @@ getObjectIdentityParts(const ObjectAddress *object, break; } + case PropgraphLabelPropertyRelationId: + { + Relation lblpropDesc; + ScanKeyData skey[1]; + SysScanDesc lblpropscan; + HeapTuple tup; + Form_pg_propgraph_label_property plpform; + ObjectAddress oa; + + lblpropDesc = table_open(PropgraphLabelPropertyRelationId, + AccessShareLock); + ScanKeyInit(&skey[0], + Anum_pg_propgraph_label_property_oid, + BTEqualStrategyNumber, F_OIDEQ, + ObjectIdGetDatum(object->objectId)); + + lblpropscan = systable_beginscan(lblpropDesc, PropgraphLabelPropertyObjectIndexId, + true, NULL, 1, skey); + + tup = systable_getnext(lblpropscan); + if (!HeapTupleIsValid(tup)) + { + if (!missing_ok) + elog(ERROR, "could not find tuple for label property %u", + object->objectId); + + systable_endscan(lblpropscan); + table_close(lblpropDesc, AccessShareLock); + break; + } + + plpform = (Form_pg_propgraph_label_property) GETSTRUCT(tup); + + ObjectAddressSet(oa, PropgraphElementLabelRelationId, plpform->plpellabelid); + appendStringInfoString(&buffer, getObjectIdentityParts(&oa, objname, + objargs, false)); + + systable_endscan(lblpropscan); + table_close(lblpropDesc, AccessShareLock); + break; + } + case PropgraphLabelRelationId: { HeapTuple tup; diff --git a/src/test/regress/expected/event_trigger.out b/src/test/regress/expected/event_trigger.out index 065f586310f..ed8d5df397e 100644 --- a/src/test/regress/expected/event_trigger.out +++ b/src/test/regress/expected/event_trigger.out @@ -173,6 +173,23 @@ NOTICE: test_event_trigger: ddl_command_end CREATE USER MAPPING alter default privileges for role regress_evt_user revoke delete on tables from regress_evt_user; NOTICE: test_event_trigger: ddl_command_end ALTER DEFAULT PRIVILEGES +-- DROP PROPERTY GRAPH should work with event trigger in place +CREATE TABLE t1x (a int PRIMARY KEY, b text); +NOTICE: test_event_trigger: ddl_command_start CREATE TABLE +NOTICE: test_event_trigger: ddl_command_end CREATE TABLE +CREATE TABLE t2x (i int PRIMARY KEY, j text); +NOTICE: test_event_trigger: ddl_command_start CREATE TABLE +NOTICE: test_event_trigger: ddl_command_end CREATE TABLE +CREATE PROPERTY GRAPH gx + VERTEX TABLES ( + t1x KEY (a) LABEL l1 PROPERTIES (b AS p1), + t2x KEY (i) LABEL l2 PROPERTIES (j AS p1) +); +NOTICE: test_event_trigger: ddl_command_end CREATE PROPERTY GRAPH +DROP PROPERTY GRAPH gx; +NOTICE: test_event_trigger: ddl_command_end DROP PROPERTY GRAPH +DROP TABLE t1x, t2x; +NOTICE: test_event_trigger: ddl_command_end DROP TABLE -- alter owner to non-superuser should fail alter event trigger regress_event_trigger owner to regress_evt_user; ERROR: permission denied to change owner of event trigger "regress_event_trigger" diff --git a/src/test/regress/expected/object_address.out b/src/test/regress/expected/object_address.out index 97227d67a54..729c3537f25 100644 --- a/src/test/regress/expected/object_address.out +++ b/src/test/regress/expected/object_address.out @@ -593,7 +593,9 @@ WITH objects (classid, objid, objsubid) AS (VALUES ('pg_parameter_acl'::regclass, 0, 0), -- no parameter ACL ('pg_policy'::regclass, 0, 0), -- no policy ('pg_propgraph_element'::regclass, 0, 0), -- no property graph element + ('pg_propgraph_element_label'::regclass, 0, 0), -- no property graph element label ('pg_propgraph_label'::regclass, 0, 0), -- no property graph label + ('pg_propgraph_label_property'::regclass, 0, 0), -- no property graph label property ('pg_propgraph_property'::regclass, 0, 0), -- no property graph property ('pg_publication'::regclass, 0, 0), -- no publication ('pg_publication_namespace'::regclass, 0, 0), -- no publication namespace @@ -653,6 +655,8 @@ ORDER BY objects.classid, objects.objid, objects.objsubid; ("(""parameter ACL"",,,)")|("(""parameter ACL"",,)")|NULL ("(""property graph element"",,,)")|("(""property graph element"",,)")|NULL ("(""property graph label"",,,)")|("(""property graph label"",,)")|NULL +("(""property graph element label"",,,)")|("(""property graph element label"",,)")|NULL ("(""property graph property"",,,)")|("(""property graph property"",,)")|NULL +("(""property graph label property"",,,)")|("(""property graph label property"",,)")|NULL -- restore normal output mode \a\t diff --git a/src/test/regress/sql/event_trigger.sql b/src/test/regress/sql/event_trigger.sql index 32e9bb58c5e..271f443378b 100644 --- a/src/test/regress/sql/event_trigger.sql +++ b/src/test/regress/sql/event_trigger.sql @@ -143,6 +143,19 @@ create user mapping for regress_evt_user server useless_server; alter default privileges for role regress_evt_user revoke delete on tables from regress_evt_user; +-- DROP PROPERTY GRAPH should work with event trigger in place +CREATE TABLE t1x (a int PRIMARY KEY, b text); +CREATE TABLE t2x (i int PRIMARY KEY, j text); + +CREATE PROPERTY GRAPH gx + VERTEX TABLES ( + t1x KEY (a) LABEL l1 PROPERTIES (b AS p1), + t2x KEY (i) LABEL l2 PROPERTIES (j AS p1) +); + +DROP PROPERTY GRAPH gx; +DROP TABLE t1x, t2x; + -- alter owner to non-superuser should fail alter event trigger regress_event_trigger owner to regress_evt_user; diff --git a/src/test/regress/sql/object_address.sql b/src/test/regress/sql/object_address.sql index 1bbe9457c1c..620dacf1045 100644 --- a/src/test/regress/sql/object_address.sql +++ b/src/test/regress/sql/object_address.sql @@ -282,7 +282,9 @@ WITH objects (classid, objid, objsubid) AS (VALUES ('pg_parameter_acl'::regclass, 0, 0), -- no parameter ACL ('pg_policy'::regclass, 0, 0), -- no policy ('pg_propgraph_element'::regclass, 0, 0), -- no property graph element + ('pg_propgraph_element_label'::regclass, 0, 0), -- no property graph element label ('pg_propgraph_label'::regclass, 0, 0), -- no property graph label + ('pg_propgraph_label_property'::regclass, 0, 0), -- no property graph label property ('pg_propgraph_property'::regclass, 0, 0), -- no property graph property ('pg_publication'::regclass, 0, 0), -- no publication ('pg_publication_namespace'::regclass, 0, 0), -- no publication namespace -- 2.34.1 --gtUR827Uq8d5gVsQ-- ^ permalink raw reply [nested|flat] 75+ messages in thread
end of thread, other threads:[~2026-04-23 09:27 UTC | newest] Thread overview: 75+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-17 13:13 [PATCH] Lock upgrade without deadlocks. Antonin Houska <[email protected]> 2026-04-23 09:27 [PATCH v2] Fix DROP PROPERTY GRAPH "unsupported object class" error Bertrand Drouvot <[email protected]>
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