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Commitc172b7b

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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 parentb8a91d9 commitc172b7b

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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
@@ -499,7 +499,7 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
499499
* Remove stale transactions, if any.
500500
*/
501501
ExpireOldKnownAssignedTransactionIds(running->oldestRunningXid);
502-
StandbyReleaseOldLocks(running->oldestRunningXid);
502+
StandbyReleaseOldLocks(running->xcnt,running->xids);
503503

504504
/*
505505
* If our snapshot is already valid, nothing else to do...
@@ -553,12 +553,6 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
553553
* OK, we need to initialise from the RunningTransactionsData record
554554
*/
555555

556-
/*
557-
* Release any locks belonging to old transactions that are not running
558-
* according to the running-xacts record.
559-
*/
560-
StandbyReleaseOldLocks(running->nextXid);
561-
562556
/*
563557
* Nobody else is running yet, but take locks anyhow
564558
*/

‎src/backend/storage/ipc/standby.c

Lines changed: 75 additions & 35 deletions
Original file line numberDiff line numberDiff line change
@@ -525,7 +525,9 @@ StandbyAcquireAccessExclusiveLock(TransactionId xid, Oid dbOid, Oid relOid)
525525
LOCKTAGlocktag;
526526

527527
/* Already processed? */
528-
if (TransactionIdDidCommit(xid)||TransactionIdDidAbort(xid))
528+
if (!TransactionIdIsValid(xid)||
529+
TransactionIdDidCommit(xid)||
530+
TransactionIdDidAbort(xid))
529531
return;
530532

531533
elog(trace_recovery(DEBUG4),
@@ -607,34 +609,86 @@ StandbyReleaseLockTree(TransactionId xid, int nsubxids, TransactionId *subxids)
607609
}
608610

609611
/*
610-
* StandbyReleaseLocksMany
611-
*Release standby locks held by XIDs < removeXid
612-
*
613-
* If keepPreparedXacts is true, keep prepared transactions even if
614-
* they're older than removeXid
612+
* Called at end of recovery and when we see a shutdown checkpoint.
615613
*/
616-
staticvoid
617-
StandbyReleaseLocksMany(TransactionIdremoveXid,boolkeepPreparedXacts)
614+
void
615+
StandbyReleaseAllLocks(void)
616+
{
617+
ListCell*cell,
618+
*prev,
619+
*next;
620+
LOCKTAGlocktag;
621+
622+
elog(trace_recovery(DEBUG2),"release all standby locks");
623+
624+
prev=NULL;
625+
for (cell=list_head(RecoveryLockList);cell;cell=next)
626+
{
627+
xl_standby_lock*lock= (xl_standby_lock*)lfirst(cell);
628+
629+
next=lnext(cell);
630+
631+
elog(trace_recovery(DEBUG4),
632+
"releasing recovery lock: xid %u db %u rel %u",
633+
lock->xid,lock->dbOid,lock->relOid);
634+
SET_LOCKTAG_RELATION(locktag,lock->dbOid,lock->relOid);
635+
if (!LockRelease(&locktag,AccessExclusiveLock, true))
636+
elog(LOG,
637+
"RecoveryLockList contains entry for lock no longer recorded by lock manager: xid %u database %u relation %u",
638+
lock->xid,lock->dbOid,lock->relOid);
639+
RecoveryLockList=list_delete_cell(RecoveryLockList,cell,prev);
640+
pfree(lock);
641+
}
642+
}
643+
644+
/*
645+
* StandbyReleaseOldLocks
646+
*Release standby locks held by XIDs that aren't running, as long
647+
*as they're not prepared transactions.
648+
*/
649+
void
650+
StandbyReleaseOldLocks(intnxids,TransactionId*xids)
618651
{
619652
ListCell*cell,
620653
*prev,
621654
*next;
622655
LOCKTAGlocktag;
623656

624-
/*
625-
* Release all matching locks.
626-
*/
627657
prev=NULL;
628658
for (cell=list_head(RecoveryLockList);cell;cell=next)
629659
{
630660
xl_standby_lock*lock= (xl_standby_lock*)lfirst(cell);
661+
boolremove= false;
631662

632663
next=lnext(cell);
633664

634-
if (!TransactionIdIsValid(removeXid)||TransactionIdPrecedes(lock->xid,removeXid))
665+
Assert(TransactionIdIsValid(lock->xid));
666+
667+
if (StandbyTransactionIdIsPrepared(lock->xid))
668+
remove= false;
669+
else
670+
{
671+
inti;
672+
boolfound= false;
673+
674+
for (i=0;i<nxids;i++)
675+
{
676+
if (lock->xid==xids[i])
677+
{
678+
found= true;
679+
break;
680+
}
681+
}
682+
683+
/*
684+
* If its not a running transaction, remove it.
685+
*/
686+
if (!found)
687+
remove= true;
688+
}
689+
690+
if (remove)
635691
{
636-
if (keepPreparedXacts&&StandbyTransactionIdIsPrepared(lock->xid))
637-
continue;
638692
elog(trace_recovery(DEBUG4),
639693
"releasing recovery lock: xid %u db %u rel %u",
640694
lock->xid,lock->dbOid,lock->relOid);
@@ -651,27 +705,6 @@ StandbyReleaseLocksMany(TransactionId removeXid, bool keepPreparedXacts)
651705
}
652706
}
653707

654-
/*
655-
* Called at end of recovery and when we see a shutdown checkpoint.
656-
*/
657-
void
658-
StandbyReleaseAllLocks(void)
659-
{
660-
elog(trace_recovery(DEBUG2),"release all standby locks");
661-
StandbyReleaseLocksMany(InvalidTransactionId, false);
662-
}
663-
664-
/*
665-
* StandbyReleaseOldLocks
666-
*Release standby locks held by XIDs < removeXid, as long
667-
*as they're not prepared transactions.
668-
*/
669-
void
670-
StandbyReleaseOldLocks(TransactionIdremoveXid)
671-
{
672-
StandbyReleaseLocksMany(removeXid, true);
673-
}
674-
675708
/*
676709
* --------------------------------------------------------------------
677710
*Recovery handling for Rmgr RM_STANDBY_ID
@@ -813,6 +846,13 @@ standby_desc(StringInfo buf, uint8 xl_info, char *rec)
813846
* Later, when we apply the running xact data we must be careful to ignore
814847
* transactions already committed, since those commits raced ahead when
815848
* making WAL entries.
849+
*
850+
* The loose timing also means that locks may be recorded that have a
851+
* zero xid, since xids are removed from procs before locks are removed.
852+
* So we must prune the lock list down to ensure we hold locks only for
853+
* currently running xids, performed by StandbyReleaseOldLocks().
854+
* Zero xids should no longer be possible, but we may be replaying WAL
855+
* from a time when they were possible.
816856
*/
817857
void
818858
LogStandbySnapshot(TransactionId*nextXid)

‎src/backend/storage/lmgr/lock.c

Lines changed: 11 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3190,8 +3190,18 @@ GetRunningTransactionLocks(int *nlocks)
31903190
PGPROC*proc=proclock->tag.myProc;
31913191
PGXACT*pgxact=&ProcGlobal->allPgXact[proc->pgprocno];
31923192
LOCK*lock=proclock->tag.myLock;
3193+
TransactionIdxid=pgxact->xid;
31933194

3194-
accessExclusiveLocks[index].xid=pgxact->xid;
3195+
/*
3196+
* Don't record locks for transactions if we know they have already
3197+
* issued their WAL record for commit but not yet released lock.
3198+
* It is still possible that we see locks held by already complete
3199+
* transactions, if they haven't yet zeroed their xids.
3200+
*/
3201+
if (!TransactionIdIsValid(xid))
3202+
continue;
3203+
3204+
accessExclusiveLocks[index].xid=xid;
31953205
accessExclusiveLocks[index].dbOid=lock->tag.locktag_field1;
31963206
accessExclusiveLocks[index].relOid=lock->tag.locktag_field2;
31973207

‎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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