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help / color / mirror / Atom feedFrom: Tatsuo Ishii <ishii@postgresql.org>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Remove redundant null-treatment check in window function dedup.
Date: Sun, 19 Jul 2026 01:51:34 +0000
Message-ID: <E1wlGgp-0003FH-0Z@gemulon.postgresql.org> (raw)
Remove redundant null-treatment check in window function dedup.
Commit 25a30bbd423 (IGNORE NULLS / RESPECT NULLS for window functions)
made ExecInitWindowAgg() treat two otherwise-equal window functions as
duplicates only when their ignore_nulls settings also matched:
if (i <= wfuncno && wfunc->ignore_nulls == perfunc[i].ignore_nulls)
That extra term reads WindowStatePerFuncData.ignore_nulls, but the field
was never populated when a per-function entry was filled in, so it stayed
zero from palloc0_array(). Consequently a duplicate call carrying
IGNORE NULLS or an explicit RESPECT NULLS never matched an identical
earlier entry and was needlessly given its own per-function slot and
evaluated twice. (Results stayed correct; this was a missed sharing, not
a wrong answer.)
The extra term is in fact redundant. WindowFunc.ignore_nulls is a plain
scalar field with no pg_node_attr, so _equalWindowFunc() already compares
it; the preceding equal() call therefore never matches two WindowFuncs
that differ only in null treatment. If equal() matches, ignore_nulls
necessarily matched too, so the term can never change the outcome, and
WindowStatePerFuncData.ignore_nulls existed only to feed it.
Rather than populate the shadow field, drop the redundant term and the
field (and adjust the now-stale comment) and let equal() do the work.
That fixes the same bug while removing the hand-maintained duplicate
state that caused it, so it cannot silently drift again.
Author: Chao Li <li.evan.chao@gmail.com>
Co-authored-by: Ewan Young <kdbase.hack@gmail.com>
Reviewed-by: Tatsuo Ishii <ishii@postgresql.org>
Discussion: https://postgr.es/m/5D2C9081-5DFE-4E27-AB14-7358238EA1BC%40gmail.com
Backpatch-through: 19
Branch
------
REL_19_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/829bacaeb323e4811eb804b5e4e29f643a0c619d
Modified Files
--------------
src/backend/executor/nodeWindowAgg.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: ishii@postgresql.org, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Remove redundant null-treatment check in window function dedup.
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