Re: Removing unneeded self joins

Andrei Lepikhov <a.lepikhov@postgrespro.ru>

From: Andrei Lepikhov <a.lepikhov@postgrespro.ru>

To: Alexander Korotkov <aekorotkov@gmail.com>, Alexander Lakhin <exclusion@gmail.com>, Richard Guo <guofenglinux@gmail.com>

Cc: "Gregory Stark (as CFM)" <stark.cfm@gmail.com>, Michał Kłeczek <michal@kleczek.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>

Date: 2024-05-02T09:44:54Z

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

0001-Forbid-self-join-elimination-on-table-sampling-scans.patch (text/x-patch) patch 0001

On 5/1/24 18:59, Alexander Korotkov wrote:
> I think we probably could forbid SJE for the tables with TABLESAMPLE
> altogether.  Please, check the attached patch.
Your patch looks good to me. I added some comments and test case into 
the join.sql.

One question for me is: Do we anticipate other lateral self-references 
except the TABLESAMPLE case? Looking into the extract_lateral_references 
implementation, I see the only RTE_SUBQUERY case to be afraid of. But we 
pull up subqueries before extracting lateral references. So, if we have 
a reference to a subquery, it means we will not flatten this subquery 
and don't execute SJE. Do we need more code, as you have written in the 
first patch?

-- 
regards,
Andrei Lepikhov
Postgres Professional