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Commit6467661

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Fix bug in HashAgg's selective-column-spilling logic.
Commit 230230223 taught nodeAgg.c that, when spilling tuples frommemory in an oversized hash aggregation, it only needed to spillinput columns referenced in the node's tlist and quals. Unfortunately,that's wrong: we also have to save the grouping columns. The erroris masked in common cases because the grouping columns also appearin the tlist, but that's not necessarily true. The main categoryof plans where it's not true seem to come from semijoins ("WHEREoutercol IN (SELECT innercol FROM innertable)") where the innercolneeds an implicit promotion to make it comparable to the outercol.The grouping column will be "innercol::promotedtype", but thatexpression appears nowhere in the Agg node's own tlist and quals;only the bare "innercol" is found in the tlist.I spent quite a bit of time looking for a suitable regression testcase for this, without much success. If the number of distinctvalues of the innercol is large enough to make spilling happen,the planner tends to prefer a non-HashAgg plan, at least forproblem sizes that are reasonable to use in the regression tests.So, no new regression test. However, this patch does demonstrablyfix the originally-reported test case.Per report from s.p.e (at) gmx-topmail.de. Backpatch to v13where the troublesome code came in.Discussion:https://postgr.es/m/trinity-1c565d44-159f-488b-a518-caf13883134f-1611835701633@3c-app-gmx-bap78
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‎src/backend/executor/nodeAgg.c

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1399,7 +1399,7 @@ project_aggregates(AggState *aggstate)
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}
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/*
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*Walk tlist and qual to find referenced colnos, dividing them into
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*Find input-tuple columns that are needed, dividing them into
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* aggregated and unaggregated sets.
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*/
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staticvoid
@@ -1412,9 +1412,15 @@ find_cols(AggState *aggstate, Bitmapset **aggregated, Bitmapset **unaggregated)
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context.aggregated=NULL;
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context.unaggregated=NULL;
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/* Examine tlist and quals */
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(void)find_cols_walker((Node*)agg->plan.targetlist,&context);
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(void)find_cols_walker((Node*)agg->plan.qual,&context);
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/* In some cases, grouping columns will not appear in the tlist */
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for (inti=0;i<agg->numCols;i++)
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context.unaggregated=bms_add_member(context.unaggregated,
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agg->grpColIdx[i]);
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*aggregated=context.aggregated;
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*unaggregated=context.unaggregated;
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}

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