From 69f75bf825f83dc506e73cf88f0adde541c39004 Mon Sep 17 00:00:00 2001 From: Etsuro Fujita Date: Thu, 15 Dec 2022 21:15:00 +0900 Subject: [PATCH] postgres_fdw: Fix assertion in estimate_path_cost_size(). Commit 08d2d58a2 added this assertion assuming that the retrieved_rows estimate for a foreign relation is set to at least one row in estimate_path_cost_size(), but the assumption isn't correct because if the relation is a foreign table with tuples=0, the estimate would be set to 0 in there when using local stats, and if the query's WHERE clause has a NULL condition, the estimate could be set to 0 in there when using remote estimates. (Note: even in the latter case the assertion could be reachable when costing foreign final paths.) Repair. Per bug #17713 from Robins Tharakan. This patch was already applied to v13 or later; apply it to v12 as well where the aforementioned commit was added. Thanks to Richard Guo for investigation. Discussion: http://postgr.es/m/17713-92cce66de7e81c04%40postgresql.org Discussion: http://postgr.es/m/CAEP4nAza%2B0fTCLkgkKYux3JDo3tUBTQORehP%2BaCxSNURpSFpHw%40mail.gmail.com --- contrib/postgres_fdw/expected/postgres_fdw.out | 18 ++++++++++++++++++ contrib/postgres_fdw/postgres_fdw.c | 2 +- contrib/postgres_fdw/sql/postgres_fdw.sql | 12 ++++++++++++ 3 files changed, 31 insertions(+), 1 deletion(-) diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out index 92cff268ca..e3cc20ff4b 100644 --- a/contrib/postgres_fdw/expected/postgres_fdw.out +++ b/contrib/postgres_fdw/expected/postgres_fdw.out @@ -590,6 +590,24 @@ SELECT t1."C 1", t2.c1, t3.c1 FROM "S 1"."T 1" t1 full join ft1 t2 full join ft2 RESET enable_hashjoin; RESET enable_nestloop; +-- Test executing assertion in estimate_path_cost_size() that makes sure that +-- retrieved_rows for foreign rel re-used to cost pre-sorted foreign paths is +-- a sensible value even when the rel has tuples=0 +CREATE TABLE loct_empty (c1 int NOT NULL, c2 text); +CREATE FOREIGN TABLE ft_empty (c1 int NOT NULL, c2 text) + SERVER loopback OPTIONS (table_name 'loct_empty'); +INSERT INTO loct_empty + SELECT id, 'AAA' || to_char(id, 'FM000') FROM generate_series(1, 100) id; +DELETE FROM loct_empty; +ANALYZE ft_empty; +EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft_empty ORDER BY c1; + QUERY PLAN +------------------------------------------------------------------------------- + Foreign Scan on public.ft_empty + Output: c1, c2 + Remote SQL: SELECT c1, c2 FROM public.loct_empty ORDER BY c1 ASC NULLS LAST +(3 rows) + -- =================================================================== -- WHERE with remotely-executable conditions -- =================================================================== diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c index a4d0377f31..7aa6d7c549 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -2749,7 +2749,7 @@ estimate_path_cost_size(PlannerInfo *root, */ if (fpinfo->rel_startup_cost >= 0 && fpinfo->rel_total_cost >= 0) { - Assert(fpinfo->retrieved_rows >= 1); + Assert(fpinfo->retrieved_rows >= 0); rows = fpinfo->rows; retrieved_rows = fpinfo->retrieved_rows; diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql index 3118ac5468..6cc8b251cc 100644 --- a/contrib/postgres_fdw/sql/postgres_fdw.sql +++ b/contrib/postgres_fdw/sql/postgres_fdw.sql @@ -285,6 +285,18 @@ SELECT t1."C 1", t2.c1, t3.c1 FROM "S 1"."T 1" t1 full join ft1 t2 full join ft2 RESET enable_hashjoin; RESET enable_nestloop; +-- Test executing assertion in estimate_path_cost_size() that makes sure that +-- retrieved_rows for foreign rel re-used to cost pre-sorted foreign paths is +-- a sensible value even when the rel has tuples=0 +CREATE TABLE loct_empty (c1 int NOT NULL, c2 text); +CREATE FOREIGN TABLE ft_empty (c1 int NOT NULL, c2 text) + SERVER loopback OPTIONS (table_name 'loct_empty'); +INSERT INTO loct_empty + SELECT id, 'AAA' || to_char(id, 'FM000') FROM generate_series(1, 100) id; +DELETE FROM loct_empty; +ANALYZE ft_empty; +EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft_empty ORDER BY c1; + -- =================================================================== -- WHERE with remotely-executable conditions -- ===================================================================