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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 15:30:02 +09:00
parent 6467661b6d
commit 984384129b
3 changed files with 31 additions and 1 deletions
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12
contrib/postgres_fdw/sql/postgres_fdw.sql
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@ -298,6 +298,18 @@ 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
-- ===================================================================