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Stabilize test case added by commit f61db909d.

2021年6月20日 15:48:44 +0000 (11:48 -0400)

Buildfarm members ayu and tern have sometimes shown a different
plan than expected for this query. I'd been unable to reproduce
that before today, but I finally realized what is happening.
If there is a concurrent open transaction (probably an autovacuum
run in the buildfarm, but this can also be arranged manually),
then the index entries for the rows removed by the DELETE a few
lines up are not killed promptly, causing a change in the planner's
estimate of the extremal value of ft2.c1, which moves the rowcount
estimate for "c1 > 1100" by enough to change the join plan from
nestloop to hash.

To fix, change the query condition to "c1 > 1000", causing the
hash plan to be preferred whether or not a concurrent open
transaction exists. Since this UPDATE is tailored to be a no-op,
nothing else changes.

Report: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=ayu&dt=2021年06月09日%2022%3A45%3A48
Report: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=ayu&dt=2021年06月13日%2022%3A38%3A18
Report: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=tern&dt=2021年06月20日%2004%3A55%3A36

contrib/postgres_fdw/expected/postgres_fdw.out patch | blob | blame | history

contrib/postgres_fdw/sql/postgres_fdw.sql patch | blob | blame | history

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out

index 858e5d4a388ce3a2166f90c626b73537ff8da92c..cc1cca30067f1518008a4cdcad036264ee91b9c2 100644 (file)

--- a/contrib/postgres_fdw/expected/postgres_fdw.out

+++ b/contrib/postgres_fdw/expected/postgres_fdw.out

@@ -5535,7 +5535,7 @@ UPDATE ft2 AS target SET (c2) = (

-- but a SET clause that can't be

EXPLAIN (VERBOSE, COSTS OFF)

UPDATE ft2 d SET c2 = CASE WHEN random() >= 0 THEN d.c2 ELSE 0 END

- FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1100;

+ FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1000;

QUERY PLAN

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Update on public.ft2 d

@@ -5543,19 +5543,22 @@ UPDATE ft2 d SET c2 = CASE WHEN random() >= 0 THEN d.c2 ELSE 0 END

-> Foreign Scan

Output: CASE WHEN (random() >= '0'::double precision) THEN d.c2 ELSE 0 END, d.ctid, d.*, t.*

Relations: (public.ft2 d) INNER JOIN (public.ft2 t)

- Remote SQL: SELECT r1.c2, r1.ctid, CASE WHEN (r1.*)::text IS NOT NULL THEN ROW(r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8) END, CASE WHEN (r2.*)::text IS NOT NULL THEN ROW(r2."C 1", r2.c2, r2.c3, r2.c4, r2.c5, r2.c6, r2.c7, r2.c8) END FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r1."C 1" = r2."C 1")) AND ((r1."C 1" > 1100)))) FOR UPDATE OF r1

- -> Nested Loop

+ Remote SQL: SELECT r1.c2, r1.ctid, CASE WHEN (r1.*)::text IS NOT NULL THEN ROW(r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8) END, CASE WHEN (r2.*)::text IS NOT NULL THEN ROW(r2."C 1", r2.c2, r2.c3, r2.c4, r2.c5, r2.c6, r2.c7, r2.c8) END FROM ("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (((r1."C 1" = r2."C 1")) AND ((r1."C 1" > 1000)))) FOR UPDATE OF r1

+ -> Hash Join

Output: d.c2, d.ctid, d.*, t.*

+ Hash Cond: (d.c1 = t.c1)

-> Foreign Scan on public.ft2 d

Output: d.c2, d.ctid, d.*, d.c1

- Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8, ctid FROM "S 1"."T 1" WHERE (("C 1" > 1100)) ORDER BY "C 1" ASC NULLS LAST FOR UPDATE

- -> Foreign Scan on public.ft2 t

+ Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8, ctid FROM "S 1"."T 1" WHERE (("C 1" > 1000)) ORDER BY "C 1" ASC NULLS LAST FOR UPDATE

+ -> Hash

Output: t.*, t.c1

- Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE ((1ドル::integer = "C 1"))

-(14 rows)

+ -> Foreign Scan on public.ft2 t

+ Output: t.*, t.c1

+ Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1"

+(17 rows)

UPDATE ft2 d SET c2 = CASE WHEN random() >= 0 THEN d.c2 ELSE 0 END

- FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1100;

+ FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1000;

-- Test UPDATE/DELETE with WHERE or JOIN/ON conditions containing

-- user-defined operators/functions

ALTER SERVER loopback OPTIONS (DROP extensions);

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql

index 34a67d716052c151c2a2dbb788eae909ee374982..8983209c74bac8b673aa5c7006e17b78b8b7081f 100644 (file)

--- a/contrib/postgres_fdw/sql/postgres_fdw.sql

+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -1259,9 +1259,9 @@ UPDATE ft2 AS target SET (c2) = (

-- but a SET clause that can't be

EXPLAIN (VERBOSE, COSTS OFF)

UPDATE ft2 d SET c2 = CASE WHEN random() >= 0 THEN d.c2 ELSE 0 END

- FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1100;

+ FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1000;

UPDATE ft2 d SET c2 = CASE WHEN random() >= 0 THEN d.c2 ELSE 0 END

- FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1100;

+ FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1000;

-- Test UPDATE/DELETE with WHERE or JOIN/ON conditions containing

-- user-defined operators/functions

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