Re: Removing unneeded self joins

Alexander Korotkov <aekorotkov@gmail.com>

From: Alexander Korotkov <aekorotkov@gmail.com>

To: Alexander Lakhin <exclusion@gmail.com>

Cc: Andrei Lepikhov <a.lepikhov@postgrespro.ru>, "Gregory Stark (as CFM)" <stark.cfm@gmail.com>, Michał Kłeczek <michal@kleczek.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Richard Guo <guofenglinux@gmail.com>

Date: 2024-01-09T06:08:37Z

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

On Tue, Jan 9, 2024 at 6:00 AM Alexander Lakhin <exclusion@gmail.com> wrote:
> 09.01.2024 01:09, Alexander Korotkov wrote:
> > Fixed in 30b4955a46.
>
> Thank you for fixing that!
>
> I've found another anomaly coined with d3d55ce57. This query:
> CREATE TABLE t(a int PRIMARY KEY, b int);
> INSERT INTO t VALUES  (1, 1), (2, 1);
>
> WITH t1 AS (SELECT * FROM t)
> UPDATE t SET b = t1.b + 1 FROM t1
> WHERE t.a = t1.a RETURNING t.a, t1.b;
>
> gives "ERROR:  variable not found in subplan target lists" on d3d55ce57, but
> starting from a7928a57b it gives an incorrect result:
>   a | b
> ---+---
>   1 | 2
>   2 | 2
> (2 rows)

I see.  It seems to be not safe to apply SJE to the modify table
target relation because it could use a different snapshot for the
RETURNING clause.  I think we should just forbid SJE to involve the
modify table target relation.  I'm planning to fix this later today.

------
Regards,
Alexander Korotkov