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: 2024-07-15T06:08:43Z

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

On 7/15/24 12:31, jian he wrote:
> hi.
> Here is the latest patch (v6),
> I've made the following changes.
> 
> * disallow original Query->resultRelation participate in SJE.
> for SELECT, nothing is changed. for UPDATE/DELETE/MERGE
> we can do:
> EXPLAIN (COSTS OFF)
> UPDATE sj sq SET b = sq.b + sz.a FROM (select s1.* from sj s1 join sj
> s2 on s1.a = s2.a) as sz
> WHERE sz.a = sq.a;
> 
> here, only "(select s1.* from sj s1 join sj s2 on s1.a = s2.a)" can
> apply to SJE.
> 
> but for now we cannot apply SJE to
> EXPLAIN (COSTS OFF)
> UPDATE sj sq SET b = sq.b + sz.a FROM sj as sz WHERE sz.a = sq.a;
> 
> so the EPQ abnormality issue[1] won't happen.
> 
> 
> * add a new function: ChangeVarNodesExtended for
> address concerns in  [2]
I see you still stay with the code line:
if (omark && imark && omark->markType != imark->markType)

It is definitely an error. What if omark is NULL, but imark is not? Why 
not to skip this pair of relids? Or, at least, insert an assertion to 
check that you filtered it earlier.

-- 
regards, Andrei Lepikhov