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Commit8572cc4

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Resolve timing issue with logging locks for Hot Standby.
We log AccessExclusiveLocks for replay onto standby nodes,but because of timing issues on ProcArray it is possible tolog a lock that is still held by a just committed transactionthat is very soon to be removed. To avoid any timing issue weavoid applying locks made by transactions with InvalidXid.Simon Riggs, bug report Tom Lane, diagnosis Pavan Deolasee
1 parentb896e1e commit8572cc4

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4 files changed

+88
-44
lines changed

4 files changed

+88
-44
lines changed

‎src/backend/storage/ipc/procarray.c‎

Lines changed: 1 addition & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -466,7 +466,7 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
466466
* Remove stale transactions, if any.
467467
*/
468468
ExpireOldKnownAssignedTransactionIds(running->oldestRunningXid);
469-
StandbyReleaseOldLocks(running->oldestRunningXid);
469+
StandbyReleaseOldLocks(running->xcnt,running->xids);
470470

471471
/*
472472
* If our snapshot is already valid, nothing else to do...
@@ -520,12 +520,6 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
520520
* OK, we need to initialise from the RunningTransactionsData record
521521
*/
522522

523-
/*
524-
* Release any locks belonging to old transactions that are not running
525-
* according to the running-xacts record.
526-
*/
527-
StandbyReleaseOldLocks(running->nextXid);
528-
529523
/*
530524
* Nobody else is running yet, but take locks anyhow
531525
*/

‎src/backend/storage/ipc/standby.c‎

Lines changed: 75 additions & 35 deletions
Original file line numberDiff line numberDiff line change
@@ -524,7 +524,9 @@ StandbyAcquireAccessExclusiveLock(TransactionId xid, Oid dbOid, Oid relOid)
524524
LOCKTAGlocktag;
525525

526526
/* Already processed? */
527-
if (TransactionIdDidCommit(xid)||TransactionIdDidAbort(xid))
527+
if (!TransactionIdIsValid(xid)||
528+
TransactionIdDidCommit(xid)||
529+
TransactionIdDidAbort(xid))
528530
return;
529531

530532
elog(trace_recovery(DEBUG4),
@@ -606,34 +608,86 @@ StandbyReleaseLockTree(TransactionId xid, int nsubxids, TransactionId *subxids)
606608
}
607609

608610
/*
609-
* StandbyReleaseLocksMany
610-
*Release standby locks held by XIDs < removeXid
611-
*
612-
* If keepPreparedXacts is true, keep prepared transactions even if
613-
* they're older than removeXid
611+
* Called at end of recovery and when we see a shutdown checkpoint.
614612
*/
615-
staticvoid
616-
StandbyReleaseLocksMany(TransactionIdremoveXid,boolkeepPreparedXacts)
613+
void
614+
StandbyReleaseAllLocks(void)
615+
{
616+
ListCell*cell,
617+
*prev,
618+
*next;
619+
LOCKTAGlocktag;
620+
621+
elog(trace_recovery(DEBUG2),"release all standby locks");
622+
623+
prev=NULL;
624+
for (cell=list_head(RecoveryLockList);cell;cell=next)
625+
{
626+
xl_standby_lock*lock= (xl_standby_lock*)lfirst(cell);
627+
628+
next=lnext(cell);
629+
630+
elog(trace_recovery(DEBUG4),
631+
"releasing recovery lock: xid %u db %u rel %u",
632+
lock->xid,lock->dbOid,lock->relOid);
633+
SET_LOCKTAG_RELATION(locktag,lock->dbOid,lock->relOid);
634+
if (!LockRelease(&locktag,AccessExclusiveLock, true))
635+
elog(LOG,
636+
"RecoveryLockList contains entry for lock no longer recorded by lock manager: xid %u database %u relation %u",
637+
lock->xid,lock->dbOid,lock->relOid);
638+
RecoveryLockList=list_delete_cell(RecoveryLockList,cell,prev);
639+
pfree(lock);
640+
}
641+
}
642+
643+
/*
644+
* StandbyReleaseOldLocks
645+
*Release standby locks held by XIDs that aren't running, as long
646+
*as they're not prepared transactions.
647+
*/
648+
void
649+
StandbyReleaseOldLocks(intnxids,TransactionId*xids)
617650
{
618651
ListCell*cell,
619652
*prev,
620653
*next;
621654
LOCKTAGlocktag;
622655

623-
/*
624-
* Release all matching locks.
625-
*/
626656
prev=NULL;
627657
for (cell=list_head(RecoveryLockList);cell;cell=next)
628658
{
629659
xl_standby_lock*lock= (xl_standby_lock*)lfirst(cell);
660+
boolremove= false;
630661

631662
next=lnext(cell);
632663

633-
if (!TransactionIdIsValid(removeXid)||TransactionIdPrecedes(lock->xid,removeXid))
664+
Assert(TransactionIdIsValid(lock->xid));
665+
666+
if (StandbyTransactionIdIsPrepared(lock->xid))
667+
remove= false;
668+
else
669+
{
670+
inti;
671+
boolfound= false;
672+
673+
for (i=0;i<nxids;i++)
674+
{
675+
if (lock->xid==xids[i])
676+
{
677+
found= true;
678+
break;
679+
}
680+
}
681+
682+
/*
683+
* If its not a running transaction, remove it.
684+
*/
685+
if (!found)
686+
remove= true;
687+
}
688+
689+
if (remove)
634690
{
635-
if (keepPreparedXacts&&StandbyTransactionIdIsPrepared(lock->xid))
636-
continue;
637691
elog(trace_recovery(DEBUG4),
638692
"releasing recovery lock: xid %u db %u rel %u",
639693
lock->xid,lock->dbOid,lock->relOid);
@@ -650,27 +704,6 @@ StandbyReleaseLocksMany(TransactionId removeXid, bool keepPreparedXacts)
650704
}
651705
}
652706

653-
/*
654-
* Called at end of recovery and when we see a shutdown checkpoint.
655-
*/
656-
void
657-
StandbyReleaseAllLocks(void)
658-
{
659-
elog(trace_recovery(DEBUG2),"release all standby locks");
660-
StandbyReleaseLocksMany(InvalidTransactionId, false);
661-
}
662-
663-
/*
664-
* StandbyReleaseOldLocks
665-
*Release standby locks held by XIDs < removeXid, as long
666-
*as they're not prepared transactions.
667-
*/
668-
void
669-
StandbyReleaseOldLocks(TransactionIdremoveXid)
670-
{
671-
StandbyReleaseLocksMany(removeXid, true);
672-
}
673-
674707
/*
675708
* --------------------------------------------------------------------
676709
*Recovery handling for Rmgr RM_STANDBY_ID
@@ -812,6 +845,13 @@ standby_desc(StringInfo buf, uint8 xl_info, char *rec)
812845
* Later, when we apply the running xact data we must be careful to ignore
813846
* transactions already committed, since those commits raced ahead when
814847
* making WAL entries.
848+
*
849+
* The loose timing also means that locks may be recorded that have a
850+
* zero xid, since xids are removed from procs before locks are removed.
851+
* So we must prune the lock list down to ensure we hold locks only for
852+
* currently running xids, performed by StandbyReleaseOldLocks().
853+
* Zero xids should no longer be possible, but we may be replaying WAL
854+
* from a time when they were possible.
815855
*/
816856
void
817857
LogStandbySnapshot(TransactionId*nextXid)

‎src/backend/storage/lmgr/lock.c‎

Lines changed: 11 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2355,8 +2355,18 @@ GetRunningTransactionLocks(int *nlocks)
23552355
{
23562356
PGPROC*proc=proclock->tag.myProc;
23572357
LOCK*lock=proclock->tag.myLock;
2358+
TransactionIdxid=proc->xid;
23582359

2359-
accessExclusiveLocks[index].xid=proc->xid;
2360+
/*
2361+
* Don't record locks for transactions if we know they have already
2362+
* issued their WAL record for commit but not yet released lock.
2363+
* It is still possible that we see locks held by already complete
2364+
* transactions, if they haven't yet zeroed their xids.
2365+
*/
2366+
if (!TransactionIdIsValid(xid))
2367+
continue;
2368+
2369+
accessExclusiveLocks[index].xid=xid;
23602370
accessExclusiveLocks[index].dbOid=lock->tag.locktag_field1;
23612371
accessExclusiveLocks[index].relOid=lock->tag.locktag_field2;
23622372

‎src/include/storage/standby.h‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -48,7 +48,7 @@ extern void StandbyAcquireAccessExclusiveLock(TransactionId xid, Oid dbOid, Oid
4848
externvoidStandbyReleaseLockTree(TransactionIdxid,
4949
intnsubxids,TransactionId*subxids);
5050
externvoidStandbyReleaseAllLocks(void);
51-
externvoidStandbyReleaseOldLocks(TransactionIdremoveXid);
51+
externvoidStandbyReleaseOldLocks(intnxids,TransactionId*xids);
5252

5353
/*
5454
* XLOG message types

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