From be99485b94e9f4560f0d8c8f1ed4afc258f75b08 Mon Sep 17 00:00:00 2001 From: Andrew Gierth Date: Wed, 6 Nov 2019 04:13:30 +0000 Subject: [PATCH] Request small targetlist for input to WindowAgg. WindowAgg will potentially store large numbers of input rows into tuplestores to allow access to other rows in the frame. If the input is coming via an explicit Sort node, then unneeded columns will already have been discarded (since Sort requests a small tlist); but there are idioms like COUNT(*) OVER () that result in the input not being sorted at all, and cases where the input is being sorted by some means other than a Sort; if we don't request a small tlist, then WindowAgg'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 --- src/backend/optimizer/plan/createplan.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c index 5f6d2bad7b..5f629adeb2 100644 --- a/src/backend/optimizer/plan/createplan.c +++ b/src/backend/optimizer/plan/createplan.c @@ -2216,10 +2216,13 @@ create_windowagg_plan(PlannerInfo *root, WindowAggPath *best_path) ListCell *lc; /* - * WindowAgg can project, so no need to be terribly picky about child - * tlist, but we do need grouping columns to be available + * Choice of tlist here is motivated by the fact that WindowAgg will be + * storing the input rows of window frames in a tuplestore; it therefore + * behooves us to request a small tlist to avoid wasting space. We do of + * course need grouping columns to be available. */ - subplan = create_plan_recurse(root, best_path->subpath, CP_LABEL_TLIST); + subplan = create_plan_recurse(root, best_path->subpath, + CP_LABEL_TLIST | CP_SMALL_TLIST); tlist = build_path_tlist(root, &best_path->path);