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Commit21946ac

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Fix corner case where SELECT FOR UPDATE could return a row twice.
In READ COMMITTED mode, if a SELECT FOR UPDATE discovers it has to redoWHERE-clause checking on rows that have been updated since the SELECT'ssnapshot, it invokes EvalPlanQual processing to do that. If this firstoccurs within a non-first child table of an inheritance tree, the previouscoding could accidentally re-return a matching row from an earlier,already-scanned child table. (And, to add insult to injury, I think thiscould make it miss returning a row that should have been returned, if theupdated row that this happens on should still have passed the WHERE qual.)Per report from Kyotaro Horiguchi; the added isolation test is based on histest case.This has been broken for quite awhile, so back-patch to all supportedbranches.
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‎src/backend/executor/nodeLockRows.c

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Original file line numberDiff line numberDiff line change
@@ -160,7 +160,29 @@ ExecLockRows(LockRowsState *node)
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*/
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if (!epq_started)
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{
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ListCell*lc2;
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EvalPlanQualBegin(&node->lr_epqstate,estate);
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/*
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* Ensure that rels with already-visited rowmarks are told
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* not to return tuples during the first EPQ test. We can
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* exit this loop once it reaches the current rowmark;
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* rels appearing later in the list will be set up
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* correctly by the EvalPlanQualSetTuple call at the top
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* of the loop.
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*/
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foreach(lc2,node->lr_arowMarks)
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{
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ExecAuxRowMark*aerm2= (ExecAuxRowMark*)lfirst(lc2);
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if (lc2==lc)
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break;
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EvalPlanQualSetTuple(&node->lr_epqstate,
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aerm2->rowmark->rti,
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NULL);
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}
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epq_started= true;
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}
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