Horton

Re: Removing unneeded self joins

Alexander Korotkov <aekorotkov@gmail.com>

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From: Alexander Korotkov <aekorotkov@gmail.com>
To: Alena Rybakina <a.rybakina@postgrespro.ru>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tom Lane <tgl@sss.pgh.pa.us>, 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: 2025-02-12T23:00:41Z
Lists: pgsql-hackers

Commits

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  1. Remove GUC_NOT_IN_SAMPLE from enable_self_join_elimination

  2. Put enable_self_join_elimination into postgresql.conf.sample

  3. Get rid of ojrelid local variable in remove_rel_from_query()

  4. Implement Self-Join Elimination

  5. Revert: Remove useless self-joins

  6. Replace lateral references to removed rels in subqueries

  7. Replace relids in lateral subquery parse tree during SJE

  8. Forbid SJE with result relation

  9. Fix misuse of RelOptInfo.unique_for_rels cache by SJE

  10. Replace the relid in some missing fields during SJE

  11. Revert 56-bit relfilenode change and follow-up commits.

  12. Stabilize timetz test across DST transitions.

  13. Speed up finding EquivalenceClasses for a given set of rels

  14. Fix mark-and-restore-skipping test case to not be a self-join.

Attachments

Hi!

On Tue, Feb 11, 2025 at 5:31 PM Alena Rybakina
<a.rybakina@postgrespro.ru> wrote:
> Hi! Thank you for the work with this subject, I think it is really
> important.
>
> On 10.02.2025 22:58, Alexander Korotkov wrote:
> > 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?
> >
> I didn't find any mistakes, I just have a refactoring remark. I think
> the part where we add non-redundant expressions with the
> binfo_candidates, jinfo_candidates
> check can be moved to a separate function, otherwise the code is very
> repetitive in this place. I did it and attached diff file

Thank you.  I've integrated that into a patch.  However, I've to
change keep_rinfo_list to be passed by pointer to
add_non_redundant_clauses(), because it might be changed in
distribute_restrictinfo_to_rels().  Without that there is a case of
duplicated clause in regression tests.

I've changed 'inner' and 'outer' vise versa in
remove_self_joins_one_group() for better readability (I believe that
was discussed upthread but lost).  Also, I did a round of improvement
for comments and commit message.

------
Regards,
Alexander Korotkov
Supabase