From b33c141cc52b5dfdf06dea1c36874a5842bada8f Mon Sep 17 00:00:00 2001 From: Etsuro Fujita Date: Fri, 7 Jun 2024 17:45:04 +0900 Subject: postgres_fdw: Refuse to send FETCH FIRST WITH TIES to remote servers. Previously, when considering LIMIT pushdown, postgres_fdw failed to check whether the query has this clause, which led to pushing false LIMIT clauses, causing incorrect results. This clause has been supported since v13, so we need to do a remote-version check before deciding that it will be safe to push such a clause, but we do not currently have a way to do the check (without accessing the remote server); disable pushing such a clause for now. Oversight in commit 357889eb1. Back-patch to v13, where that commit added the support. Per bug #18467 from Onder Kalaci. Patch by Japin Li, per a suggestion from Tom Lane, with some changes to the comments by me. Review by Onder Kalaci, Alvaro Herrera, and me. Discussion: https://postgr.es/m/18467-7bb89084ff03a08d%40postgresql.org --- contrib/postgres_fdw/expected/postgres_fdw.out | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'contrib/postgres_fdw/expected') diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out index d7fdc6b8829..f105859aa0d 100644 --- a/contrib/postgres_fdw/expected/postgres_fdw.out +++ b/contrib/postgres_fdw/expected/postgres_fdw.out @@ -1047,6 +1047,27 @@ SELECT * FROM ft1 t1 WHERE t1.c1 === t1.c2 order by t1.c2 limit 1; 1 | 1 | 00001 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1 | 1 | foo (1 row) +-- Ensure we don't ship FETCH FIRST .. WITH TIES +EXPLAIN (VERBOSE, COSTS OFF) +SELECT t1.c2 FROM ft1 t1 WHERE t1.c1 > 960 ORDER BY t1.c2 FETCH FIRST 2 ROWS WITH TIES; + QUERY PLAN +------------------------------------------------------------------------------------------------- + Limit + Output: c2 + -> Foreign Scan on public.ft1 t1 + Output: c2 + Remote SQL: SELECT c2 FROM "S 1"."T 1" WHERE (("C 1" > 960)) ORDER BY c2 ASC NULLS LAST +(5 rows) + +SELECT t1.c2 FROM ft1 t1 WHERE t1.c1 > 960 ORDER BY t1.c2 FETCH FIRST 2 ROWS WITH TIES; + c2 +---- + 0 + 0 + 0 + 0 +(4 rows) + -- Test CASE pushdown EXPLAIN (VERBOSE, COSTS OFF) SELECT c1,c2,c3 FROM ft2 WHERE CASE WHEN c1 > 990 THEN c1 END < 1000 ORDER BY c1; -- cgit v1.2.3