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Suppress unnecessary explicit sorting for EPQ mergejoin path

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When building a ForeignPath for a joinrel, if there's a possibility
that EvalPlanQual will be executed, we must identify a suitable path
for EPQ checks.  If the outer or inner path of the chosen path is a
ForeignPath representing a pushed-down join, we replace it with its
fdw_outerpath to ensure that the EPQ check path consists entirely of
local joins.

If the chosen path is a MergePath, and its outer or inner path is a
ForeignPath that is not already well enough ordered, the MergePath
will have non-NIL outersortkeys or innersortkeys indicating the
desired ordering to be created by an explicit Sort node.  If we then
replace the outer or inner path with its corresponding fdw_outerpath,
and that path is already sufficiently ordered, we end up in an
inconsistent state: the MergePath has non-NIL outersortkeys or
innersortkeys, and its input path is already properly ordered.  This
inconsistency can result in an Assert failure or the addition of a
redundant Sort node.

To fix, check if the new outer or inner path of a MergePath is already
properly sorted, and set its outersortkeys or innersortkeys to NIL if
so.

Bug: #18902
Reported-by: Nikita Kalinin <n.kalinin@postgrespro.ru>
Author: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: Tender Wang <tndrwang@gmail.com>
Discussion: https://postgr.es/m/18902-71c1bed2b9f7c46f@postgresql.org
This commit is contained in:
Richard Guo
2025-05-08 18:20:18 +09:00
parent 9fef27a83b
commit 773db22269
3 changed files with 102 additions and 0 deletions
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5
contrib/postgres_fdw/sql/postgres_fdw.sql
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@ -715,6 +715,11 @@ SELECT * FROM ft1, ft2, ft4, ft5, local_tbl WHERE ft1.c1 = ft2.c1 AND ft1.c2 = f
AND ft1.c2 = ft5.c1 AND ft1.c2 = local_tbl.c1 AND ft1.c1 < 100 AND ft2.c1 < 100 FOR UPDATE;
SELECT * FROM ft1, ft2, ft4, ft5, local_tbl WHERE ft1.c1 = ft2.c1 AND ft1.c2 = ft4.c1
AND ft1.c2 = ft5.c1 AND ft1.c2 = local_tbl.c1 AND ft1.c1 < 100 AND ft2.c1 < 100 FOR UPDATE;
EXPLAIN (VERBOSE, COSTS OFF)
SELECT * FROM ft1, ft4, ft5, local_tbl WHERE ft1.c1 = ft4.c1 AND ft1.c1 = ft5.c1
AND ft1.c2 = local_tbl.c1 AND ft1.c1 < 100 AND ft5.c1 < 100 FOR UPDATE;
SELECT * FROM ft1, ft4, ft5, local_tbl WHERE ft1.c1 = ft4.c1 AND ft1.c1 = ft5.c1
AND ft1.c2 = local_tbl.c1 AND ft1.c1 < 100 AND ft5.c1 < 100 FOR UPDATE;
RESET enable_nestloop;
RESET enable_hashjoin;