Horton

Re: Removing unneeded self joins

Andrei Lepikhov <a.lepikhov@postgrespro.ru>

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From: Andrei Lepikhov <a.lepikhov@postgrespro.ru>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: "Gregory Stark (as CFM)" <stark.cfm@gmail.com>, Michał Kłeczek <michal@kleczek.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, "a.rybakina" <a.rybakina@postgrespro.ru>
Date: 2023-10-13T02:55:13Z
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 →

  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 12/10/2023 18:32, Alexander Korotkov wrote:
> On Thu, Oct 5, 2023 at 12:17 PM Andrei Lepikhov
>> We have almost the results we wanted to have. But in the last explain
>> you can see that nothing happened with the OR clause. We should use the
>> expression mutator instead of walker to handle such clauses. But It
>> doesn't process the RestrictInfo node ... I'm inclined to put a solution
>> of this issue off for a while.
> 
> OK.  I think it doesn't worth to eliminate IS NULL quals with this
> complexity (at least at this stage of work).

Yeah. I think It would be meaningful in the case of replacing also 
nested x IS NOT NULL with nothing. But it requires using a mutator 
instead of the walker and may be done more accurately next time.

> I made improvements over the code.  Mostly new comments, grammar
> corrections of existing comments and small refactoring.

Great!

> Also, I found that the  suggestion from David Rowley [1] to qsort
> array of relations to faster find duplicates is still unaddressed.
> I've implemented it.  That helps to evade quadratic complexity with
> large number of relations.

I see. The thread is too long so far, thanks for the catch.

> Also I've incorporated improvements from Alena Rybakina except one for
> skipping SJ removal when no SJ quals is found.  It's not yet clear for
> me if this check fix some cases. But at least optimization got skipped
> in some useful cases (as you can see in regression tests).

Agree. I wouldn't say I like it too. But also, I suggest skipping some 
unnecessary assertions proposed in that patch:
Assert(toKeep->relid != -1); - quite strange. Why -1? Why not all the 
negative numbers, at least?
Assert(is_opclause(orinfo->clause)); - above we skip clauses with 
rinfo->mergeopfamilies == NIL. Each mergejoinable clause is already 
checked as is_opclause.
All these changes (see in the attachment) are optional.

-- 
regards,
Andrey Lepikhov
Postgres Professional