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Commit8f779a1

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Reset lastOverflowedXid on standby when needed
Currently, lastOverflowedXid is never reset. It's just adjusted on newtransactions known to be overflowed. But if there are no overflowedtransactions for a long time, snapshots could be mistakenly marked assuboverflowed due to wraparound.This commit fixes this issue by resetting lastOverflowedXid when neededaltogether with KnownAssignedXids.Backpatch to all supported versions.Reported-by: Stan HuDiscussion:https://postgr.es/m/CAMBWrQ%3DFp5UAsU_nATY7EMY7NHczG4-DTDU%3DmCvBQZAQ6wa2xQ%40mail.gmail.comAuthor: Kyotaro Horiguchi, Alexander KorotkovReviewed-by: Stan Hu, Simon Riggs, Nikolay Samokhvalov, Andrey Borodin, Dmitry Dolgov
1 parent3eff168 commit8f779a1

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‎src/backend/storage/ipc/procarray.c

Lines changed: 19 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -3295,24 +3295,41 @@ ExpireTreeKnownAssignedTransactionIds(TransactionId xid, int nsubxids,
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/*
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* ExpireAllKnownAssignedTransactionIds
3298-
*Remove all entries in KnownAssignedXids
3298+
*Remove all entries in KnownAssignedXids and reset lastOverflowedXid.
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*/
33003300
void
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ExpireAllKnownAssignedTransactionIds(void)
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{
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LWLockAcquire(ProcArrayLock,LW_EXCLUSIVE);
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KnownAssignedXidsRemovePreceding(InvalidTransactionId);
3305+
3306+
/*
3307+
* Reset lastOverflowedXid. Currently, lastOverflowedXid has no use after
3308+
* the call of this function. But do this for unification with what
3309+
* ExpireOldKnownAssignedTransactionIds() do.
3310+
*/
3311+
procArray->lastOverflowedXid=InvalidTransactionId;
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LWLockRelease(ProcArrayLock);
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}
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/*
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* ExpireOldKnownAssignedTransactionIds
3310-
*Remove KnownAssignedXids entries preceding the given XID
3317+
*Remove KnownAssignedXids entries preceding the given XID and
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*potentially reset lastOverflowedXid.
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*/
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void
33133321
ExpireOldKnownAssignedTransactionIds(TransactionIdxid)
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{
33153323
LWLockAcquire(ProcArrayLock,LW_EXCLUSIVE);
3324+
3325+
/*
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* Reset lastOverflowedXid if we know all transactions that have been
3327+
* possibly running are being gone. Not doing so could cause an incorrect
3328+
* lastOverflowedXid value, which makes extra snapshots be marked as
3329+
* suboverflowed.
3330+
*/
3331+
if (TransactionIdPrecedes(procArray->lastOverflowedXid,xid))
3332+
procArray->lastOverflowedXid=InvalidTransactionId;
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KnownAssignedXidsRemovePreceding(xid);
33173334
LWLockRelease(ProcArrayLock);
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}

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