Horton

Re: MergeAppend could consider sorting cheapest child path

Alexander Korotkov <aekorotkov@gmail.com>

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From: Alexander Korotkov <aekorotkov@gmail.com>
To: Andrei Lepikhov <lepihov@gmail.com>
Cc: Alexander Pyhalov <a.pyhalov@postgrespro.ru>, Andy Fan <zhihuifan1213@163.com>, Bruce Momjian <bruce@momjian.us>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Nikita Malakhov <HukuToc@gmail.com>
Date: 2025-09-07T11:26:17Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Mostly-cosmetic adjustments to estimate_multivariate_bucketsize().

  2. Consider fractional paths in generate_orderedappend_paths

Attachments

On Fri, Sep 5, 2025 at 11:45 AM Andrei Lepikhov <lepihov@gmail.com> wrote:
>
> On 1/9/2025 22:26, Alexander Korotkov wrote:
> > On Thu, Jul 31, 2025 at 5:20 PM Andrei Lepikhov <lepihov@gmail.com> wrote:
> >> See this minor correction in the attachment. postgres_fdw tests are
> >> stable now.
> >
> > I have another idea.  What if we allow MergeAppend paths only when at
> > least one subpath is preordered.  This trick also allow us to exclude
> > MergeAppend(Sort) dominating Sort(Append).  I see the regression tests
> > changes now have much less volume and looks more reasonable.  What do
> > you think?
> I believe a slight mistake has been made with the total_has_ordered /
> startup_has_ordered parameters, which has caused unnecessary test
> changes in inherit.out (See updated patch in the attachment). Although
> not the best test in general (it depends on the autovacuum), it
> highlighted the case where a startup-optimal strategy is necessary, even
> when a fractional-optimal path is available, which may lead to continue
> of the discussion [1].>
> > Also, do you think get_cheapest_fractional_path_for_pathkeys_ext() and
> > get_cheapest_path_for_pathkeys_ext() should consider incremental sort?
> >   The revised patch teaches them to do so.
> Following 55a780e9476 [2] it should be considered, of course.

Great, thank you for catching this.  The diff of costs is attached.  I
see the costs now are better or within the fuzz factor.

------
Regards,
Alexander Korotkov
Supabase