Re: apply_scanjoin_target_to_paths and partitionwise join - Mailing list pgsql-hackers

On Wed, May 22, 2024 at 3:57 PM Ashutosh Bapat
<ashutosh.bapat.oss@gmail.com> wrote:
> I will create patches for the back-branches once the patch for master is in a committable state.

AFAIU, this patch prevents apply_scanjoin_target_to_paths() from
discarding old paths of partitioned joinrels.  Therefore, we can
retain non-partitionwise join paths if the cheapest path happens to be
among them.

One concern from me is that if the cheapest path of a joinrel is a
partitionwise join path, following this approach could lead to
undesirable cross-platform plan variations, as detailed in the
original comment.

Is there a specific query that demonstrates benefits from this change?
I'm curious about scenarios where a partitionwise join runs slower
than a non-partitionwise join.

Thanks
Richard