Re: Removing unneeded self joins
Andrei Lepikhov <a.lepikhov@postgrespro.ru>
Commits
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Remove GUC_NOT_IN_SAMPLE from enable_self_join_elimination
- 717d0e8dd945 18.0 landed
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Put enable_self_join_elimination into postgresql.conf.sample
- c2d329260cd8 18.0 landed
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Get rid of ojrelid local variable in remove_rel_from_query()
- e167191dc146 18.0 landed
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Implement Self-Join Elimination
- fc069a3a6319 18.0 cited
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Revert: Remove useless self-joins
- d1d286d83c0e 17.0 landed
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Replace lateral references to removed rels in subqueries
- 466979ef031a 17.0 landed
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Replace relids in lateral subquery parse tree during SJE
- 489072ab7a9e 17.0 landed
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Forbid SJE with result relation
- 8c441c082797 17.0 landed
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Fix misuse of RelOptInfo.unique_for_rels cache by SJE
- 30b4955a4668 17.0 landed
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Replace the relid in some missing fields during SJE
- a7928a57b9f0 17.0 landed
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Revert 56-bit relfilenode change and follow-up commits.
- a448e49bcbe4 16.0 cited
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Stabilize timetz test across DST transitions.
- 4a071afbd056 14.0 cited
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Speed up finding EquivalenceClasses for a given set of rels
- 3373c7155350 13.0 cited
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Fix mark-and-restore-skipping test case to not be a self-join.
- 24d08f3c0a1f 12.0 landed
On 2/7/21 01:56, Hywel Carver wrote:
> On Wed, Jun 30, 2021 at 12:21 PM Andrey Lepikhov
> <a.lepikhov@postgrespro.ru <mailto:a.lepikhov@postgrespro.ru>> wrote:
> I think, here we could ask more general question: do we want to
> remove a
> 'IS NOT NULL' clause from the clause list if the rest of the list
> implicitly implies it?
>
>
> My suggestion was not to remove it, but to avoid adding it in the first
> place. When your optimisation has found a join on a group of columns
> under a uniqueness constraint, you would do something like this (forgive
> the pseudo-code)
>
> foreach(column, join_clause) {
> if(column.nullable) { // This condition is what I'm suggesting is added
> add_null_test(column, IS_NOT_NULL);
> }
> }
>
> But it may be that that's not possible or practical at this point in the
> code.
I think, such option will require to implement a new machinery to prove
that arbitrary column couldn't produce NULL value.
--
regards,
Andrey Lepikhov
Postgres Professional