Re: BUG #18830: ExecInitMerge Segfault on MERGE

Amit Langote <amitlangote09(at)gmail(dot)com> 于2025年3月12日周三 20:24写道：

> Thanks -- I’ve studied the code and I agree with the conclusion: when
> all result relations are pruned, we still need to lock and process the
> first one to preserve executor invariants.
>
> Your examples with ExecMerge() and ExecInitPartitionInfo() make the
> consequences of missing resultRelInfo[0] pretty clear. Locking and
> including the first result relation, even if pruned, seems like the
> most straightforward way to maintain correctness without deeper
> structural changes.
>
> I've come up with the attached. I'll still need to add a test case.
>

It looks good to me, on a quick read-through.

We now don't have merge into ... not match ... test case in
partition_prune.sql
In [1], I figured out a query that could trigger a crash. It may be used as
the test case.

create table part_abc (a int, b text, c bool) partition by list (a);
create table part_abc_1 (b text, a int, c bool);
create table part_abc_2 (a int, c bool, b text);
alter table part_abc attach partition part_abc_1 for values in (1);
alter table part_abc attach partition part_abc_2 for values in (2);
insert into part_abc values (1, 'b', true);
insert into part_abc values (2, 'c', true);
create view part_abc_view as select * from part_abc where b <> 'a' with
check option;
create function stable_one() returns int as $$ begin return 1; end; $$
language plpgsql stable;

Above SQLs are already in parition_prune.sql, only need the below SQLs.
explain (costs off)
merge into part_abc_view pt
using (select stable_one() + 2 as pid) as q join part_abc_1 pt1 on (true)
on pt.a = stable_one() +2
when not matched then insert values(1, 'd', false);
merge into part_abc_view pt
using (select stable_one() + 2 as pid) as q join part_abc_1 pt1 on (true)
on pt.a = stable_one() +2
when not matched then insert values(1, 'd', false);

[1]
https://www.postgresql.org/message-id/CAHewXN%3DS5nqVMqoYpFXe8OykqDC-r22vG7RvDN-VFamY7XcVTw%40mail.gmail.com
--
Thanks,
Tender Wang