Re: WIP: Aggregation push-down

Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> wrote:

> > 1) v14-0001-Introduce-RelInfoList-structure.patch
> > -------------------------------------------------
> >
> > - I'm not entirely sure why we need this change. We had the list+hash
> > before, so I assume we do this because we need the output functions?
>
> I believe that this is what Tom proposed in [1], see "Maybe an appropriate
> preliminary patch is to refactor the support code ..." near the end of that
> message. The point is that now we need two lists: one for "plain" relations
> and one for grouped ones.
>
>
> I guess what Toms suggested[1] is to store the the grouped ones into
> root->upper_rels rather than a separated member, see fetch_upper_rel
> or UpperRelationKind. If we do need the list+hash method for long list lookup,
> we can merge it into upper_rels. If we want this benefits at other place rather
> than root->upper_rels, we can store a generic type in RelInfoList, looks currently
> it is bounded to RelAggInfo besides RelOptInfo. But overall, personally I think we can
> ignore such optimization at the first stage to save the attention of the core reviewers
> since they are too precious :) Just FYI
>
> [1] https://www.postgresql.org/message-id/9726.1542577439@sss.pgh.pa.us

Hm, you seem to be right, not sure why I missed the point. I thought that the
reason Tom doesn't like storing the grouped relations in simple_rel_array is
that we only need the grouped base relations inside query_planner(), but
simple_rel_array is used higher in the stack. So I introduced a new field and
used it only in query_planner() and subroutines.

Yes, it's better to use root->upper_rels than to introduce the new field. I'll
adjust the patch. Thanks.

--
Antonin Houska
Web: https://www.cybertec-postgresql.com