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Minor adjustments to WindowAgg startup cost code

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This is a follow-on of 3900a02c9 containing some changes which I forgot
to commit locally before forming a patch with git format-patch.

Discussion: https://postgr.es/m/CAApHDvrB0S5BMv+0-wTTqWFE-BJ0noWqTnDu9QQfjZ2VSpLv_g@mail.gmail.com
This commit is contained in:
David Rowley 2023-08-04 10:47:54 +12:00
parent 3900a02c97
commit 3fd19a9b23
1 changed files with 5 additions and 11 deletions
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16
src/backend/optimizer/path/costsize.c
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@ -2933,8 +2933,8 @@ get_windowclause_startup_tuples(PlannerInfo *root, WindowClause *wc,
* NULLs are not allowed, but currently, there's no code to
* error out if there's a NULL Const. We'll only discover
* this during execution. For now, just pretend everything is
* fine and assume that just the current row/range/group will
* be needed.
* fine and assume that just the first row/range/group will be
* needed.
*/
end_offset_value = 1.0;
}
@ -3055,15 +3055,6 @@ cost_windowagg(Path *path, PlannerInfo *root,
startup_cost = input_startup_cost;
total_cost = input_total_cost;
/*
* Estimate how many tuples we'll need to read from the subnode before we
* can output the first WindowAgg row.
*/
startup_tuples = get_windowclause_startup_tuples(root, winclause,
input_tuples);
elog(DEBUG1, "startup_tuples = %g", startup_tuples); /* XXX not for commit */
/*
* Window functions are assumed to cost their stated execution cost, plus
* the cost of evaluating their input expressions, per tuple. Since they
@ -3124,6 +3115,9 @@ cost_windowagg(Path *path, PlannerInfo *root,
* cost of the subnode, so we only need to do this when the estimated
* startup tuples is above 1.0.
*/
startup_tuples = get_windowclause_startup_tuples(root, winclause,
input_tuples);
if (startup_tuples > 1.0)
path->startup_cost += (total_cost - startup_cost) / input_tuples *
(startup_tuples - 1.0);