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

On Tue, Dec 19, 2023 at 12:30 AM PG Bug reporting form <
noreply(at)postgresql(dot)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.

I have no idea about how to fix it.

BTW, while reading the codes, I noticed two typos in simplehash.h, one
is in the comment of SH_INSERT, the other is in the comment of
SH_INSERT_HASH. Attached is a trivial patch for that.

Thanks
Richard