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Fix crash in postgres_fdw for provably-empty remote UPDATE/DELETE.

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In 86dc90056, I'd written find_modifytable_subplan with the assumption
that if the immediate child of a ModifyTable is a Result, it must be
a projecting Result with a subplan.  However, if the UPDATE or DELETE
has a provably-constant-false WHERE clause, that's not so: we'll
generate a dummy subplan with a childless Result.  Add the missing
null-check so we don't crash on such cases.

Per report from Alexander Pyhalov.

Discussion: https://postgr.es/m/b9a6f53549456b2f3e2fd150dcd79d72@postgrespro.ru
This commit is contained in:
Tom Lane 2021-07-07 15:21:25 -04:00
parent 9d2a775734
commit b9734c13f1
3 changed files with 27 additions and 1 deletions
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20
contrib/postgres_fdw/expected/postgres_fdw.out
View File

@ -6853,6 +6853,26 @@ DROP TRIGGER trig_row_before ON rem1;
DROP TRIGGER trig_row_after ON rem1;
DROP TRIGGER trig_local_before ON loc1;
-- Test direct foreign table modification functionality
EXPLAIN (verbose, costs off)
DELETE FROM rem1; -- can be pushed down
QUERY PLAN
---------------------------------------------
Delete on public.rem1
-> Foreign Delete on public.rem1
Remote SQL: DELETE FROM public.loc1
(3 rows)
EXPLAIN (verbose, costs off)
DELETE FROM rem1 WHERE false; -- currently can't be pushed down
QUERY PLAN
-------------------------------------------------------
Delete on public.rem1
Remote SQL: DELETE FROM public.loc1 WHERE ctid = $1
-> Result
Output: ctid
One-Time Filter: false
(5 rows)
-- Test with statement-level triggers
CREATE TRIGGER trig_stmt_before
BEFORE DELETE OR INSERT OR UPDATE ON rem1

4
contrib/postgres_fdw/postgres_fdw.c
View File

@ -2370,7 +2370,9 @@ find_modifytable_subplan(PlannerInfo *root,
if (subplan_index < list_length(appendplan->appendplans))
subplan = (Plan *) list_nth(appendplan->appendplans, subplan_index);
}
else if (IsA(subplan, Result) && IsA(outerPlan(subplan), Append))
else if (IsA(subplan, Result) &&
outerPlan(subplan) != NULL &&
IsA(outerPlan(subplan), Append))
{
Append *appendplan = (Append *) outerPlan(subplan);

4
contrib/postgres_fdw/sql/postgres_fdw.sql
View File

@ -1738,6 +1738,10 @@ DROP TRIGGER trig_local_before ON loc1;
-- Test direct foreign table modification functionality
EXPLAIN (verbose, costs off)
DELETE FROM rem1; -- can be pushed down
EXPLAIN (verbose, costs off)
DELETE FROM rem1 WHERE false; -- currently can't be pushed down
-- Test with statement-level triggers
CREATE TRIGGER trig_stmt_before