Re: Removing unneeded self joins

Andrei Lepikhov <lepihov@gmail.com>

From: Andrei Lepikhov <lepihov@gmail.com>

To: jian he <jian.universality@gmail.com>, Alexander Korotkov <aekorotkov@gmail.com>

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

Date: 2024-07-12T03:05:15Z

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

v4-0002-Apply-SJE-to-DML-queries-2.patch (text/x-patch) patch v4-0002

On 7/11/24 14:43, jian he wrote:
> On Tue, Jul 9, 2024 at 2:06 PM Andrei Lepikhov <lepihov@gmail.com> wrote:
>>
>> On 7/2/24 07:25, jian he wrote:
>>> to make sure it's correct, I have added a lot of tests,
>>> Some of this may be contrived, maybe some of the tests are redundant.
>> Thanks for your job!
>> I passed through the patches and have some notes:
>> 1. Patch 0001 has not been applied anymore since the previous week's
>> changes in the core. Also, there is one place with trailing whitespace.
> 
> thanks.
> because the previous thread mentioned the EPQ problem.
> in remove_useless_self_joins, i make it can only process CMD_SELECT query.
I would like to oppose here: IMO, it is just a mishap which we made 
because of a long history of patch transformations. There we lost the 
case where RowMark exists for only one of candidate relations.
Also, after review I think we don't need so many new tests. Specifically 
for DML we already have one:

EXPLAIN (COSTS OFF)
UPDATE sj sq SET b = 1 FROM sj as sz WHERE sq.a = sz.a;

And we should just add something to elaborate it a bit.
See the patch in attachment containing my proposal to improve v4-0001 
main SJE patch. I think it resolved the issue with EPQ assertion as well 
as problems with returning value.

-- 
regards, Andrei Lepikhov