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Commitdeadbf4

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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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3 files changed

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‎src/backend/executor/nodeLockRows.c

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Original file line numberDiff line numberDiff line change
@@ -161,7 +161,29 @@ 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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‎src/test/isolation/expected/eval-plan-qual.out

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Original file line numberDiff line numberDiff line change
@@ -49,3 +49,26 @@ accountid balance
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checking 600
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savings 2334
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starting permutation: readp1 writep1 readp2 c1 c2
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step readp1: SELECT tableoid::regclass, ctid, * FROM p WHERE b IN (0, 1) AND c = 0 FOR UPDATE;
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tableoid ctid a b c
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c1 (0,1) 0 0 0
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c1 (0,4) 0 1 0
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c2 (0,1) 1 0 0
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c2 (0,4) 1 1 0
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c3 (0,1) 2 0 0
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c3 (0,4) 2 1 0
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step writep1: UPDATE p SET b = -1 WHERE a = 1 AND b = 1 AND c = 0;
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step readp2: SELECT tableoid::regclass, ctid, * FROM p WHERE b IN (0, 1) AND c = 0 FOR UPDATE; <waiting ...>
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step c1: COMMIT;
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step readp2: <... completed>
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tableoid ctid a b c
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c1 (0,1) 0 0 0
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c1 (0,4) 0 1 0
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c2 (0,1) 1 0 0
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c3 (0,1) 2 0 0
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c3 (0,4) 2 1 0
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step c2: COMMIT;

‎src/test/isolation/specs/eval-plan-qual.spec

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Original file line numberDiff line numberDiff line change
@@ -8,11 +8,20 @@ setup
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{
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CREATETABLEaccounts (accountidtextPRIMARYKEY,balancenumericnotnull);
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INSERTINTOaccountsVALUES ('checking',600), ('savings',600);
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CREATETABLEp (aint,bint,cint);
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CREATETABLEc1 ()INHERITS (p);
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CREATETABLEc2 ()INHERITS (p);
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CREATETABLEc3 ()INHERITS (p);
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INSERTINTOc1SELECT0,a/3,a%3FROMgenerate_series(0,9)a;
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INSERTINTOc2SELECT1,a/3,a%3FROMgenerate_series(0,9)a;
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INSERTINTOc3SELECT2,a/3,a%3FROMgenerate_series(0,9)a;
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}
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teardown
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{
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DROPTABLEaccounts;
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DROPTABLEpCASCADE;
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}
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session"s1"
@@ -30,6 +39,11 @@ step "upsert1"{
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INSERTINTOaccountsSELECT'savings',500
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WHERENOTEXISTS (SELECT1FROMupsert);
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}
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# tests with table p check inheritance cases, specifically a bug where
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# nodeLockRows did the wrong thing when the first updated tuple was in
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# a non-first child table
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step"readp1"{SELECTtableoid::regclass,ctid,*FROMpWHEREbIN (0,1)ANDc=0FORUPDATE; }
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step"writep1"{UPDATEpSETb=-1WHEREa=1ANDb=1ANDc=0; }
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step"c1"{COMMIT; }
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session"s2"
@@ -44,6 +58,7 @@ step "upsert2"{
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INSERTINTOaccountsSELECT'savings',1234
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WHERENOTEXISTS (SELECT1FROMupsert);
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}
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step"readp2"{SELECTtableoid::regclass,ctid,*FROMpWHEREbIN (0,1)ANDc=0FORUPDATE; }
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step"c2"{COMMIT; }
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session"s3"
@@ -54,3 +69,4 @@ teardown{ COMMIT; }
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permutation"wx1""wx2""c1""c2""read"
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permutation"wy1""wy2""c1""c2""read"
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permutation"upsert1""upsert2""c1""c2""read"
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permutation"readp1""writep1""readp2""c1""c2"

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