Re: Removing unneeded self joins

Alexander Korotkov <aekorotkov@gmail.com>

From: Alexander Korotkov <aekorotkov@gmail.com>

To: Tom Lane <tgl@sss.pgh.pa.us>

Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Andrei Lepikhov <lepihov@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Richard Guo <guofenglinux@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: 2025-02-10T19:58:54Z

Lists: pgsql-hackers

Commits

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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

v12-0001-Remove-useless-self-joins.patch (application/octet-stream) patch v12-0001

Hi!

On Mon, Feb 10, 2025 at 7:19 AM Andrei Lepikhov <lepihov@gmail.com> wrote:
> On 9/2/2025 18:41, Alexander Korotkov wrote:
> > Regarding adjust_relid_set() and replace_relid().  I think they are
> > now strictly equivalent, except for the case then old relid is given
> > and not found.  In this case adjust_relid_set() returns the original
> > relids while replace_relid() returns a copy.  The behavior of
> > adjust_relid_set() appears more desirable as we don't need extra
> > copying when no modification is done.  So, I've replaced all
> > replace_relid() with adjust_relid_set().
> Ok, I glanced into it, and it makes sense to merge these routines.
> I think the comment to adjust_relid_set() should be arranged, too. See
> the attachment for a short variant of such modification.
> >
> > Also, I did some grammar correction to your new comment in tests.
> Thanks!

I've further revised adjust_relid_set() header comment.

Looking back to the work done since previous attempt to commit this to
pg17, I can highlight following.
1) We're now using more of existing infrastructure including
adjust_relid_set() and ChangeVarNodes().  The most of complexity is
still there though.
2) We've checked few ways to further simplify this patch.  But yet the
current way still feels to be best possible.
3) For sure, several bugs were fixed.

I think we could give it another chance for pg18 after some further
polishing (at least commit message still needs to be revised).  Any
thoughts on this?  Tom?

------
Regards,
Alexander Korotkov
Supabase