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postgres_fdw: Fix assertion in estimate_path_cost_size().

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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
This commit is contained in:
Etsuro Fujita 2022-12-15 21:15:00 +09:00
parent 1cca4a75ff
commit 69f75bf825
3 changed files with 31 additions and 1 deletions
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18
contrib/postgres_fdw/expected/postgres_fdw.out
View File

@ -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
-- ===================================================================

2
contrib/postgres_fdw/postgres_fdw.c
View File

@ -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;

12
contrib/postgres_fdw/sql/postgres_fdw.sql
View File

@ -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
-- ===================================================================