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Commita9056cc

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Request small targetlist for input to WindowAgg.
WindowAgg will potentially store large numbers of input rows intotuplestores to allow access to other rows in the frame. If the inputis coming via an explicit Sort node, then unneeded columns willalready have been discarded (since Sort requests a small tlist); butthere are idioms like COUNT(*) OVER () that result in the input notbeing sorted at all, and cases where the input is being sorted by somemeans other than a Sort; if we don't request a small tlist, thenWindowAgg's storage requirement is inflated by the unneeded columns.Backpatch back to 9.6, where the current tlist handling was added.(Prior to that, WindowAgg would always use a small tlist.)Discussion:https://postgr.es/m/87a7ator8n.fsf@news-spur.riddles.org.uk
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‎src/backend/optimizer/plan/createplan.c

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -2397,10 +2397,13 @@ create_windowagg_plan(PlannerInfo *root, WindowAggPath *best_path)
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ListCell*lc;
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/*
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* WindowAgg can project, so no need to be terribly picky about child
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* tlist, but we do need grouping columns to be available
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* Choice of tlist here is motivated by the fact that WindowAgg will be
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* storing the input rows of window frames in a tuplestore; it therefore
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* behooves us to request a small tlist to avoid wasting space. We do of
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* course need grouping columns to be available.
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*/
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subplan=create_plan_recurse(root,best_path->subpath,CP_LABEL_TLIST);
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subplan=create_plan_recurse(root,best_path->subpath,
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CP_LABEL_TLIST |CP_SMALL_TLIST);
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tlist=build_path_tlist(root,&best_path->path);
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