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Commit632f0fa

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Repair some flakiness in CheckTargetForConflictsIn.
When we release and reacquire SerializableXactHashLock, we must recheckwhether an R/W conflict still needs to be flagged, because it could havechanged under us in the meantime. And when we release the partitionlock, we must re-walk the list of predicate locks from the beginning,because our pointer could get invalidated under us.Bug report #5952 by Yamamoto Takashi. Patch by Kevin Grittner.
1 parent38d15f1 commit632f0fa

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‎src/backend/storage/lmgr/predicate.c

Lines changed: 24 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3757,6 +3757,17 @@ CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag)
37573757
LWLockRelease(partitionLock);
37583758
LWLockRelease(SerializablePredicateLockListLock);
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LWLockAcquire(partitionLock,LW_SHARED);
3760+
3761+
/*
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* The list may have been altered by another process
3763+
* while we weren't holding the partition lock. Start
3764+
* over at the front.
3765+
*/
3766+
nextpredlock= (PREDICATELOCK*)
3767+
SHMQueueNext(&(target->predicateLocks),
3768+
&(target->predicateLocks),
3769+
offsetof(PREDICATELOCK,targetLink));
3770+
37603771
LWLockAcquire(SerializableXactHashLock,LW_SHARED);
37613772
}
37623773
}
@@ -3770,7 +3781,19 @@ CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag)
37703781
LWLockRelease(SerializableXactHashLock);
37713782
LWLockAcquire(SerializableXactHashLock,LW_EXCLUSIVE);
37723783

3773-
FlagRWConflict(sxact, (SERIALIZABLEXACT*)MySerializableXact);
3784+
/*
3785+
* Re-check after getting exclusive lock because the other
3786+
* transaction may have flagged a conflict.
3787+
*/
3788+
if (!SxactIsRolledBack(sxact)
3789+
&& (!SxactIsCommitted(sxact)
3790+
||TransactionIdPrecedes(GetTransactionSnapshot()->xmin,
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sxact->finishedBefore))
3792+
&& !RWConflictExists(sxact,
3793+
(SERIALIZABLEXACT*)MySerializableXact))
3794+
{
3795+
FlagRWConflict(sxact, (SERIALIZABLEXACT*)MySerializableXact);
3796+
}
37743797

37753798
LWLockRelease(SerializableXactHashLock);
37763799
LWLockAcquire(SerializableXactHashLock,LW_SHARED);

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