Re: post-freeze damage control

On Tue, Apr 9, 2024 at 8:37 AM Andrei Lepikhov
<a(dot)lepikhov(at)postgrespro(dot)ru> wrote:
> On 9/4/2024 09:12, Tom Lane wrote:
> > I have another one that I'm not terribly happy about:
> >
> > Author: Alexander Korotkov <akorotkov(at)postgresql(dot)org>
> > Branch: master [72bd38cc9] 2024-04-08 01:27:52 +0300
> >
> > Transform OR clauses to ANY expression
> Because I'm primary author of the idea, let me answer.
> >
> > I don't know that I'd call it scary exactly, but I do think it
> > was premature. A week ago there was no consensus that it was
> > ready to commit, but Alexander pushed it (or half of it, anyway)
> > despite that. A few concrete concerns:
> >
> > * Yet another planner GUC. Do we really need or want that?
> It is the most interesting question here. Looking around planner
> features designed but not applied for the same reason because they can
> produce suboptimal plans in corner cases, I think about inventing
> flag-type parameters and hiding some features that work better for
> different load types under such flagged parameters.

Yes, I have spotted this transformation could cause a bitmap scan plan
regressions in [1] and [2]. Fixing that required to treat ANY the
same as OR for bitmap scans. Andrei implemented that in [3], but that
increases planning complexity and elimitates significant part of the
advantages of OR-to-ANY transformation.

Links.
1. https://www.postgresql.org/message-id/CAPpHfduJtO0s9E%3DSHUTzrCD88BH0eik0UNog1_q3XBF2wLmH6g%40mail.gmail.com
2. https://www.postgresql.org/message-id/CAPpHfdtSXxhdv3mLOLjEewGeXJ%2BFtfhjqodn1WWuq5JLsKx48g%40mail.gmail.com
3. https://www.postgresql.org/message-id/6d27d752-db0b-4cac-9843-6ba3dd7a1e94%40postgrespro.ru

------
Regards,
Alexander Korotkov