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In postgres_fdw, don't try to ship MULTIEXPR updates to remote server.

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In a statement like "UPDATE remote_tab SET (x,y) = (SELECT ...)",
we'd conclude that the statement could be directly executed remotely,
because the sub-SELECT is in a resjunk tlist item that's not examined
for shippability.  Currently that ends up crashing if the sub-SELECT
contains any remote Vars.  Prevent the crash by deeming MULTIEXEC
Params to be unshippable.

This is a bit of a brute-force solution, since if the sub-SELECT
*doesn't* contain any remote Vars, the current execution technology
would work; but that's not a terribly common use-case for this syntax,
I think.  In any case, we generally don't try to ship sub-SELECTs, so
it won't surprise anybody that this doesn't end up as a remote direct
update.  I'd be inclined to see if that general limitation can be fixed
before worrying about this case further.

Per report from Lukáš Sobotka.

Back-patch to 9.6.  9.5 had MULTIEXPR, but we didn't try to perform
remote direct updates then, so the case didn't arise anyway.

Discussion: https://postgr.es/m/CAJif3k+iA_ekBB5Zw2hDBaE1wtiQa4LH4_JUXrrMGwTrH0J01Q@mail.gmail.com
This commit is contained in:
Tom Lane
2020-01-26 14:31:08 -05:00
parent 451f50813b
commit 43a648f57c
3 changed files with 67 additions and 0 deletions
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20
contrib/postgres_fdw/sql/postgres_fdw.sql
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@ -784,6 +784,26 @@ EXPLAIN (verbose, costs off)
DELETE FROM ft2 WHERE c1 = 9999 RETURNING tableoid::regclass; -- can be pushed down
DELETE FROM ft2 WHERE c1 = 9999 RETURNING tableoid::regclass;
-- Test UPDATE with a MULTIEXPR sub-select
-- (maybe someday this'll be remotely executable, but not today)
EXPLAIN (verbose, costs off)
UPDATE ft2 AS target SET (c2, c7) = (
SELECT c2 * 10, c7
FROM ft2 AS src
WHERE target.c1 = src.c1
) WHERE c1 > 1100;
UPDATE ft2 AS target SET (c2, c7) = (
SELECT c2 * 10, c7
FROM ft2 AS src
WHERE target.c1 = src.c1
) WHERE c1 > 1100;
UPDATE ft2 AS target SET (c2) = (
SELECT c2 / 10
FROM ft2 AS src
WHERE target.c1 = src.c1
) WHERE c1 > 1100;
-- Test that trigger on remote table works as expected
CREATE OR REPLACE FUNCTION "S 1".F_BRTRIG() RETURNS trigger AS $$
BEGIN