Re: BUG #18252: Assert in CheckOpSlotCompatibility() fails when recursive union filters tuples in non-recursive term

On Tue, Dec 19, 2023 at 7:28 PM Richard Guo <guofenglinux@gmail.com> wrote:

> On Tue, Dec 19, 2023 at 12:30 AM PG Bug reporting form <
> noreply@postgresql.org> wrote:
>
>> CREATE TABLE t(i int);
>> INSERT INTO t VALUES (1), (1);
>>
>> WITH RECURSIVE rt(i) AS (
>>     SELECT * FROM t
>>     UNION
>>     SELECT * FROM rt
>> )
>> SELECT * FROM rt;
>
>
> Nice catch.  The TupleHashTable's tableslot is created as type
> TTSOpsMinimalTuple.  The RecursiveUnion's non-recursive term generates
> tuples of type TTSOpsBufferHeapTuple.  If the non-recursive term
> produces duplicate tuples, we'd find non-empty bucket when inserting the
> same key into the hashtable.  In this case we need to check to see if
> the two tuples match: one is of the hashtable's tableslot
> (TTSOpsMinimalTuple), and the other comes from the non-recursive term
> (TTSOpsBufferHeapTuple).  And the incompatible slot type would fail
> CheckOpSlotCompatibility.
>

This Assert was added in 15d8f8312:

commit 15d8f83128e15de97de61430d0b9569f5ebecc26
Author: Andres Freund <andres@anarazel.de>
Date:   Thu Nov 15 22:00:30 2018 -0800

    Verify that expected slot types match returned slot types.

So loop in Andres to have a look.

Thanks
Richard