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Commit46c333a

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Fix overly strict assertion in SummarizeOldestCommittedSxact(). There's a
race condition where SummarizeOldestCommittedSxact() is called even thoughanother backend already cleared out all finished sxact entries. That's OK,RegisterSerializableTransactionInt() can just retry getting a news xactslot from the available-list when that happens.Reported by YAMAMOTO Takashi, bug #5918.
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‎src/backend/storage/lmgr/predicate.c‎

Lines changed: 10 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1314,15 +1314,21 @@ SummarizeOldestCommittedSxact(void)
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LWLockAcquire(SerializableFinishedListLock,LW_EXCLUSIVE);
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#ifdefTEST_OLDSERXID
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/*
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* This function is only called if there are no sxact slots available.
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* Some of them must belong to old, already-finished transactions, so
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* there should be something in FinishedSerializableTransactions list
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* that we can summarize. However, there's a race condition: while we
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* were not holding any locks, a transaction might have ended and cleaned
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* up all the finished sxact entries already, freeing up their sxact
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* slots. In that case, we have nothing to do here. The caller will find
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* one of the slots released by the other backend when it retries.
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*/
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if (SHMQueueEmpty(FinishedSerializableTransactions))
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{
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LWLockRelease(SerializableFinishedListLock);
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return;
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}
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#else
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Assert(!SHMQueueEmpty(FinishedSerializableTransactions));
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#endif
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/*
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* Grab the first sxact off the finished list -- this will be the earliest

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