Horton

Re: Removing unneeded self joins

Andrei Lepikhov <a.lepikhov@postgrespro.ru>

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From: Andrey Lepikhov <a.lepikhov@postgrespro.ru>
To: Hywel Carver <hywel@skillerwhale.com>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2021-07-15T14:49:11Z
Lists: pgsql-hackers

Commits

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  1. Remove GUC_NOT_IN_SAMPLE from enable_self_join_elimination

  2. Put enable_self_join_elimination into postgresql.conf.sample

  3. Get rid of ojrelid local variable in remove_rel_from_query()

  4. Implement Self-Join Elimination

  5. Revert: Remove useless self-joins

  6. Replace lateral references to removed rels in subqueries

  7. Replace relids in lateral subquery parse tree during SJE

  8. Forbid SJE with result relation

  9. Fix misuse of RelOptInfo.unique_for_rels cache by SJE

  10. Replace the relid in some missing fields during SJE

  11. Revert 56-bit relfilenode change and follow-up commits.

  12. Stabilize timetz test across DST transitions.

  13. Speed up finding EquivalenceClasses for a given set of rels

  14. Fix mark-and-restore-skipping test case to not be a self-join.

Attachments

On 6/7/21 13:49, Hywel Carver wrote:
> On Mon, Jul 5, 2021 at 2:20 PM Andrey Lepikhov 
> <a.lepikhov@postgrespro.ru <mailto:a.lepikhov@postgrespro.ru>> wrote:
> Looking through the email chain, a previous version of this patch added 
> ~0.6% to planning time in the worst case tested - does that meet the 
> "essentially free" requirement?
I think these tests weren't full coverage of possible use cases. It will 
depend on a number of relations in the query. For the JOIN of 
partitioned tables, for example, the overhead could grow. But in the 
context of overall planning time this overhead will be small till the 
large number of relations.
Also, we made this feature optional to solve possible problems.
Rebased on 768ea9bcf9

-- 
regards,
Andrey Lepikhov
Postgres Professional