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Commitc928dc9

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Fix old visibility bug in HeapTupleSatisfiesDirty
If a tuple is locked but not updated by a concurrent transaction,HeapTupleSatisfiesDirty would return that transaction's Xid in xmax,causing callers to wait on it, when it is not necessary (in fact, if theother transaction had used a multixact instead of a plain Xid to markthe tuple, HeapTupleSatisfiesDirty would have behave differently and*not* returned the Xmax).This bug was introduced in commit3f7fbf8, dated December 1998,so it's almost 15 years old now. However, it's hard to see thismisbehave, because before we had NOWAIT the only consequence of this isthat transactions would wait for slightly more time than necessary; soit's not surprising that this hasn't been reported yet.Craig Ringer and Andres Freund
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‎src/backend/utils/time/tqual.c

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -861,7 +861,8 @@ HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Snapshot snapshot,
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if (TransactionIdIsInProgress(HeapTupleHeaderGetXmax(tuple)))
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{
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snapshot->xmax=HeapTupleHeaderGetXmax(tuple);
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if (!(tuple->t_infomask&HEAP_IS_LOCKED))
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snapshot->xmax=HeapTupleHeaderGetXmax(tuple);
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return true;
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}
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