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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
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@ -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
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RESET enable_hashjoin;
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RESET enable_nestloop;
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-- Test executing assertion in estimate_path_cost_size() that makes sure that
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-- retrieved_rows for foreign rel re-used to cost pre-sorted foreign paths is
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-- a sensible value even when the rel has tuples=0
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CREATE TABLE loct_empty (c1 int NOT NULL, c2 text);
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CREATE FOREIGN TABLE ft_empty (c1 int NOT NULL, c2 text)
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SERVER loopback OPTIONS (table_name 'loct_empty');
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INSERT INTO loct_empty
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SELECT id, 'AAA' || to_char(id, 'FM000') FROM generate_series(1, 100) id;
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DELETE FROM loct_empty;
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ANALYZE ft_empty;
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EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft_empty ORDER BY c1;
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-- ===================================================================
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-- WHERE with remotely-executable conditions
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-- ===================================================================
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