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postgres_fdw: Fix assertion in estimate_path_cost_size().

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Commit 08d2d58a2 added an assertion assuming that the retrieved_rows
estimate for a foreign relation, which is re-used to cost pre-sorted
foreign paths with local stats, is set to at least one row in
estimate_path_cost_size(), which isn't correct because if the relation
is a foreign table with tuples=0, the estimate would be set to 0 there
when not using remote estimates.

Per bug #16807 from Alexander Lakhin.  Back-patch to v13 where the
aforementioned commit went in.

Author: Etsuro Fujita
Reviewed-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/16807-9fe4e08fbaa5c7ce%40postgresql.org
This commit is contained in:
Etsuro Fujita 2021-02-05 15:30:00 +09:00
parent 0ff865fbe5
commit 5e7fa189ee
3 changed files with 31 additions and 1 deletions
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18
contrib/postgres_fdw/expected/postgres_fdw.out
View File

@ -613,6 +613,24 @@ 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

@ -2923,7 +2923,7 @@ 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

@ -309,6 +309,18 @@ 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
-- ===================================================================