Re: v12.0: ERROR: could not find pathkey item to sort

On Wed, Nov 6, 2019 at 1:51 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Amit Langote <amitlangote09@gmail.com> writes:
> > I have been thinking maybe add_child_rel_equivalences() doesn't need
> > to translate EC members that reference multiple appendrels, because
> > there top_parent_relids is always a singleton set, whereas em_relids
> > of such expressions is not?  Those half-translated expressions are
> > useless, only adding to the overhead of scanning ec_members.  I'm
> > thinking that we should apply this diff:
> > -            if (bms_overlap(cur_em->em_relids, top_parent_relids))
> > +            if (bms_is_subset(cur_em->em_relids, top_parent_relids))
>
> Meh, I'm not really convinced.  The case where this would be relevant
> is an EC generated from something like "WHERE (a.x + b.y) = c.z"
> where "a" is partitioned.  It's possible that we'd never have a use
> for a sort key corresponding to "a_child.x + b.y", but I think that's
> not obvious, and probably short-sighted.  Anyway such EC members are
> pretty rare in the first place, so we're not going to win much
> performance by trying to optimize them.

OK.

> Anyway, I've pushed the fix for Justin's problem to v12 and HEAD.
> The problem with poor planning of multiway joins that you mentioned
> in the other thread remains open, but I imagine the patches you
> posted there are going to need rebasing over this commit, so I
> set that CF entry to Waiting On Author.

Thank you.  I will send rebased patches on that thread.

Regards,
Amit