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Commited78384

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Move call to GetTopTransactionId() earlier in LockAcquire(),
removing an infrequently occurring race condition in Hot Standby.An xid must be assigned before a lock appears in shared memory,rather than immediately after, else GetRunningTransactionLocks()may see InvalidTransactionId, causing assertion failures duringlock processing on standby.Bug report and diagnosis by Fujii Masao, fix by me.
1 parentc623365 commited78384

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3 files changed

+43
-16
lines changed

3 files changed

+43
-16
lines changed

‎src/backend/storage/ipc/standby.c

Lines changed: 21 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -953,14 +953,6 @@ LogAccessExclusiveLock(Oid dbOid, Oid relOid)
953953
{
954954
xl_standby_lockxlrec;
955955

956-
/*
957-
* Ensure that a TransactionId has been assigned to this transaction. We
958-
* don't actually need the xid yet but if we don't do this then
959-
* RecordTransactionCommit() and RecordTransactionAbort() will optimise
960-
* away the transaction completion record which recovery relies upon to
961-
* release locks. It's a hack, but for a corner case not worth adding code
962-
* for into the main commit path.
963-
*/
964956
xlrec.xid=GetTopTransactionId();
965957

966958
/*
@@ -973,3 +965,24 @@ LogAccessExclusiveLock(Oid dbOid, Oid relOid)
973965

974966
LogAccessExclusiveLocks(1,&xlrec);
975967
}
968+
969+
/*
970+
* Prepare to log an AccessExclusiveLock, for use during LockAcquire()
971+
*/
972+
void
973+
LogAccessExclusiveLockPrepare(void)
974+
{
975+
/*
976+
* Ensure that a TransactionId has been assigned to this transaction,
977+
* for two reasons, both related to lock release on the standby.
978+
* First, we must assign an xid so that RecordTransactionCommit() and
979+
* RecordTransactionAbort() do not optimise away the transaction
980+
* completion record which recovery relies upon to release locks. It's
981+
* a hack, but for a corner case not worth adding code for into the
982+
* main commit path. Second, must must assign an xid before the lock
983+
* is recorded in shared memory, otherwise a concurrently executing
984+
* GetRunningTransactionLocks() might see a lock associated with an
985+
* InvalidTransactionId which we later assert cannot happen.
986+
*/
987+
(void)GetTopTransactionId();
988+
}

‎src/backend/storage/lmgr/lock.c

Lines changed: 21 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -499,6 +499,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
499499
intpartition;
500500
LWLockIdpartitionLock;
501501
intstatus;
502+
boollog_lock= false;
502503

503504
if (lockmethodid <=0||lockmethodid >=lengthof(LockMethods))
504505
elog(ERROR,"unrecognized lock method: %d",lockmethodid);
@@ -579,6 +580,24 @@ LockAcquireExtended(const LOCKTAG *locktag,
579580
returnLOCKACQUIRE_ALREADY_HELD;
580581
}
581582

583+
/*
584+
* Emit a WAL record if acquisition of this lock needs to be replayed in a
585+
* standby server. Only AccessExclusiveLocks can conflict with lock types
586+
* that read-only transactions can acquire in a standby server.
587+
*
588+
* Make sure this definition matches the one in GetRunningTransactionLocks().
589+
*
590+
* First we prepare to log, then after lock acquired we issue log record.
591+
*/
592+
if (lockmode >=AccessExclusiveLock&&
593+
locktag->locktag_type==LOCKTAG_RELATION&&
594+
!RecoveryInProgress()&&
595+
XLogStandbyInfoActive())
596+
{
597+
LogAccessExclusiveLockPrepare();
598+
log_lock= true;
599+
}
600+
582601
/*
583602
* Otherwise we've got to mess with the shared lock table.
584603
*/
@@ -868,15 +887,9 @@ LockAcquireExtended(const LOCKTAG *locktag,
868887

869888
/*
870889
* Emit a WAL record if acquisition of this lock need to be replayed in a
871-
* standby server. Only AccessExclusiveLocks can conflict with lock types
872-
* that read-only transactions can acquire in a standby server.
873-
*
874-
* Make sure this definition matches the one GetRunningTransactionLocks().
890+
* standby server.
875891
*/
876-
if (lockmode >=AccessExclusiveLock&&
877-
locktag->locktag_type==LOCKTAG_RELATION&&
878-
!RecoveryInProgress()&&
879-
XLogStandbyInfoActive())
892+
if (log_lock)
880893
{
881894
/*
882895
* Decode the locktag back to the original values, to avoid sending

‎src/include/storage/standby.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -109,6 +109,7 @@ typedef struct RunningTransactionsData
109109
typedefRunningTransactionsData*RunningTransactions;
110110

111111
externvoidLogAccessExclusiveLock(OiddbOid,OidrelOid);
112+
externvoidLogAccessExclusiveLockPrepare(void);
112113

113114
externvoidLogStandbySnapshot(TransactionId*oldestActiveXid,TransactionId*nextXid);
114115

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