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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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4
contrib/postgres_fdw/postgres_fdw.c
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@ -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);