Re: Removing unneeded self joins

jian he <jian.universality@gmail.com>

From: jian he <jian.universality@gmail.com>

To: Alexander Korotkov <aekorotkov@gmail.com>

Cc: Andrei Lepikhov <lepihov@gmail.com>, 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: 2024-07-15T05:31:33Z

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

v6-0001-Remove-useless-self-joins.patch (application/x-patch) patch v6-0001

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]


* cosmetic refactor remove_self_join_rel, match_unique_clauses,
split_selfjoin_quals functions.
changing some "foreach" to "foreach_node"


* refactor comments above (remove_self_joins_one_group ->> match_unique_clauses)
I am not 100% sure they are correct.


[1] https://postgr.es/m/flat/CAPpHfduM6X82ExT0r9UzFLJ12wOYPvRw5vT2Htq0gAPBgHhKeQ%40mail.gmail.com
[2] https://postgr.es/m/flat/CAPpHfdvBddujLDhf7TQP-djeKoG5oyFBEoLSGRsjHfGrcNFkDg%40mail.gmail.com