Re: Removing unneeded self joins

Alexander Korotkov <aekorotkov@gmail.com>

From: Alexander Korotkov <aekorotkov@gmail.com>

To: Alena Rybakina <a.rybakina@postgrespro.ru>

Cc: Andrei Lepikhov <lepihov@gmail.com>, Richard Guo <guofenglinux@gmail.com>, Ranier Vilela <ranier.vf@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, Alexander Lakhin <exclusion@gmail.com>, "Gregory Stark (as CFM)" <stark.cfm@gmail.com>, Michał Kłeczek <michal@kleczek.org>, Dean Rasheed <dean.a.rasheed@gmail.com>

Date: 2025-04-26T20:04:22Z

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 →

Remove GUC_NOT_IN_SAMPLE from enable_self_join_elimination
- 717d0e8dd945 18.0 landed
Put enable_self_join_elimination into postgresql.conf.sample
- c2d329260cd8 18.0 landed
Get rid of ojrelid local variable in remove_rel_from_query()
- e167191dc146 18.0 landed
Implement Self-Join Elimination
- fc069a3a6319 18.0 cited
Revert: Remove useless self-joins
- d1d286d83c0e 17.0 landed
Replace lateral references to removed rels in subqueries
- 466979ef031a 17.0 landed
Replace relids in lateral subquery parse tree during SJE
- 489072ab7a9e 17.0 landed
Forbid SJE with result relation
- 8c441c082797 17.0 landed
Fix misuse of RelOptInfo.unique_for_rels cache by SJE
- 30b4955a4668 17.0 landed
Replace the relid in some missing fields during SJE
- a7928a57b9f0 17.0 landed
Revert 56-bit relfilenode change and follow-up commits.
- a448e49bcbe4 16.0 cited
Stabilize timetz test across DST transitions.
- 4a071afbd056 14.0 cited
Speed up finding EquivalenceClasses for a given set of rels
- 3373c7155350 13.0 cited
Fix mark-and-restore-skipping test case to not be a self-join.
- 24d08f3c0a1f 12.0 landed

Attachments

v2-0001-Disallow-removing-placeholders-during-Self-Join-E.patch (application/octet-stream) patch v2-0001

Hi, Alena!

On Sun, Apr 6, 2025 at 12:02 AM Alena Rybakina
<a.rybakina@postgrespro.ru> wrote:
> Should we add more regression tests covering these cases?
>
> I experimented with some examples like this and noticed that it does affect cardinality estimation, though I'm not sure the impact is significant.
> I used the tables from the regression tests, so if they’re appropriate for reproducing this case, it should be straightforward to add them.

Thank you for your feedback.  I've check the cases you've provided.  I
found that the differences here are related to the SJE itself, not to
changes regarding PHVs handling.  I think it generally OK that
estimates are somewhat changed due to such significant query
transformation.  Hopefully they should be improved in the majority of
cases.

I did some improvements to PHVs patch: revised comments and commit
message.  I'm going to push it if no objections.

------
Regards,
Alexander Korotkov
Supabase