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Fix segfault during EvalPlanQual with mix of local and foreign partitions.
It's not sensible to re-evaluate a direct-modify Foreign Update or Delete
during EvalPlanQual. However, ExecInitForeignScan() can still get called
if a table mixes local and foreign partitions. EvalPlanQualStart() left
the es_result_relations array uninitialized in the child EPQ EState, but
ExecInitForeignScan() still expected to find it. That caused a segfault.
Fix by skipping the es_result_relations lookup during EvalPlanQual
processing. To make things a bit more robust, also skip the
BeginDirectModify calls, and add a runtime check that ExecForeignScan()
is not called on direct-modify foreign scans during EvalPlanQual
processing.
This is new in v14, commit 1375422c78
. Before that, EvalPlanQualStart()
copied the whole ResultRelInfo array to the EPQ EState. Backpatch to v14.
Report and diagnosis by Andrey Lepikhov.
Discussion: https://www.postgresql.org/message-id/cb2b808d-cbaa-4772-76ee-c8809bafcf3d%40postgrespro.ru
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@ -44,12 +44,22 @@ ForeignNext(ForeignScanState *node)
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TupleTableSlot *slot;
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ForeignScan *plan = (ForeignScan *) node->ss.ps.plan;
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ExprContext *econtext = node->ss.ps.ps_ExprContext;
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EState *estate = node->ss.ps.state;
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MemoryContext oldcontext;
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/* Call the Iterate function in short-lived context */
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oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
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if (plan->operation != CMD_SELECT)
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{
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/*
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* direct modifications cannot be re-evaluated, so shouldn't get here
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* during EvalPlanQual processing
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*/
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if (estate->es_epq_active != NULL)
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elog(ERROR, "cannot re-evaluate a Foreign Update or Delete during EvalPlanQual");
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slot = node->fdwroutine->IterateDirectModify(node);
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}
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else
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slot = node->fdwroutine->IterateForeignScan(node);
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MemoryContextSwitchTo(oldcontext);
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@ -223,11 +233,25 @@ ExecInitForeignScan(ForeignScan *node, EState *estate, int eflags)
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scanstate->fdw_state = NULL;
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/*
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* For the FDW's convenience, look up the modification target relation's.
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* ResultRelInfo.
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* For the FDW's convenience, look up the modification target relation's
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* ResultRelInfo. The ModifyTable node should have initialized it for us,
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* see ExecInitModifyTable.
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*
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* Don't try to look up the ResultRelInfo when EvalPlanQual is active,
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* though. Direct modififications cannot be re-evaluated as part of
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* EvalPlanQual. The lookup wouldn't work anyway because during
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* EvalPlanQual processing, EvalPlanQual only initializes the subtree
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* under the ModifyTable, and doesn't run ExecInitModifyTable.
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*/
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if (node->resultRelation > 0)
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if (node->resultRelation > 0 && estate->es_epq_active == NULL)
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{
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if (estate->es_result_relations == NULL ||
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estate->es_result_relations[node->resultRelation - 1] == NULL)
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{
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elog(ERROR, "result relation not initialized");
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}
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scanstate->resultRelInfo = estate->es_result_relations[node->resultRelation - 1];
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}
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/* Initialize any outer plan. */
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if (outerPlan(node))
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@ -238,7 +262,15 @@ ExecInitForeignScan(ForeignScan *node, EState *estate, int eflags)
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* Tell the FDW to initialize the scan.
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*/
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if (node->operation != CMD_SELECT)
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{
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/*
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* Direct modifications cannot be re-evaluated by EvalPlanQual, so
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* don't bother preparing the FDW. There can ForeignScan nodes in the
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* EvalPlanQual subtree, but ExecForeignScan should never be called.
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*/
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if (estate->es_epq_active == NULL)
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fdwroutine->BeginDirectModify(scanstate, eflags);
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}
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else
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fdwroutine->BeginForeignScan(scanstate, eflags);
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@ -255,10 +287,14 @@ void
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ExecEndForeignScan(ForeignScanState *node)
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{
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ForeignScan *plan = (ForeignScan *) node->ss.ps.plan;
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EState *estate = node->ss.ps.state;
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/* Let the FDW shut down */
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if (plan->operation != CMD_SELECT)
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{
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if (estate->es_epq_active == NULL)
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node->fdwroutine->EndDirectModify(node);
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}
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else
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node->fdwroutine->EndForeignScan(node);
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