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Commita88fe25

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Be sure to rewind the tuplestore read pointer in non-leader CTEScan nodes.
ExecInitCteScan supposed that it didn't have to do anything to the extratuplestore read pointer it gets from tuplestore_alloc_read_pointer.However, it needs this read pointer to be positioned at the start of thetuplestore, while tuplestore_alloc_read_pointer is actually defined ascloning the current position of read pointer 0. In normal situationsthat accidentally works because we initialize the whole plan tree at once,before anything gets read. But it fails in an EvalPlanQual recheck, asillustrated in bug #14328 from Dima Pavlov. To fix, just forcibly rewindthe pointer after tuplestore_alloc_read_pointer. The cost of doing so isnegligible unless the tuplestore is already in TSS_READFILE state, whichwouldn't happen in normal cases. We could consider altering tuplestore'sAPI to make that case cheaper, but that would make for a more invasiveback-patch and it doesn't seem worth it.This has been broken probably for as long as we've had CTEs, so back-patchto all supported branches.Discussion: <32468.1474548308@sss.pgh.pa.us>
1 parentc925e63 commita88fe25

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‎src/backend/executor/nodeCtescan.c

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@@ -224,9 +224,13 @@ ExecInitCteScan(CteScan *node, EState *estate, int eflags)
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{
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/* Not the leader */
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Assert(IsA(scanstate->leader,CteScanState));
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/* Create my own read pointer, and ensure it is at start */
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scanstate->readptr=
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tuplestore_alloc_read_pointer(scanstate->leader->cte_table,
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scanstate->eflags);
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tuplestore_select_read_pointer(scanstate->leader->cte_table,
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scanstate->readptr);
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tuplestore_rescan(scanstate->leader->cte_table);
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}
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/*

‎src/test/isolation/expected/eval-plan-qual.out

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@@ -163,3 +163,24 @@ ta_id ta_value tb_row
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1 newTableAValue (1,tableBValue)
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step c2: COMMIT;
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starting permutation: wrtwcte readwcte c1 c2
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step wrtwcte: UPDATE table_a SET value = 'tableAValue2' WHERE id = 1;
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step readwcte:
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WITH
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cte1 AS (
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SELECT id FROM table_b WHERE value = 'tableBValue'
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),
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cte2 AS (
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SELECT * FROM table_a
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WHERE id = (SELECT id FROM cte1)
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FOR UPDATE
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)
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SELECT * FROM cte2;
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<waiting ...>
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step c1: COMMIT;
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step c2: COMMIT;
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step readwcte: <... completed>
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id value
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1 tableAValue2

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

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@@ -103,11 +103,27 @@ step "readforss"{
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FROMtable_ata
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WHEREta.id=1FORUPDATEOFta;
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}
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step"wrtwcte"{UPDATEtable_aSETvalue='tableAValue2'WHEREid=1; }
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step"c2"{COMMIT; }
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session"s3"
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setup{BEGINISOLATIONLEVELREADCOMMITTED; }
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step"read"{SELECT*FROMaccountsORDERBYaccountid; }
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# this test exercises EvalPlanQual with a CTE, cf bug #14328
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step"readwcte"{
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WITH
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cte1AS (
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SELECTidFROMtable_bWHEREvalue='tableBValue'
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),
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cte2AS (
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SELECT*FROMtable_a
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WHEREid= (SELECTidFROMcte1)
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FORUPDATE
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)
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SELECT*FROMcte2;
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}
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teardown{COMMIT; }
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permutation"wx1""wx2""c1""c2""read"
@@ -118,3 +134,4 @@ permutation "writep2" "returningp1" "c1" "c2"
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permutation"wx2""partiallock""c2""c1""read"
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permutation"wx2""lockwithvalues""c2""c1""read"
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permutation"updateforss""readforss""c1""c2"
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permutation"wrtwcte""readwcte""c1""c2"

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