Horton

Re: POC: GROUP BY optimization

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Andrei Lepikhov <a.lepikhov@postgrespro.ru>, PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Teodor Sigaev <teodor@sigaev.ru>, David Rowley <dgrowleyml@gmail.com>, "a.rybakina" <a.rybakina@postgrespro.ru>, Белялов Дамир Наилевич <d.belyalov@postgrespro.ru>
Date: 2023-12-27T04:27:39Z
Lists: pgsql-hackers

Commits

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  1. Restore preprocess_groupclause()

  2. Rename PathKeyInfo to GroupByOrdering

  3. Add invariants check to get_useful_group_keys_orderings()

  4. Fix asymmetry in setting EquivalenceClass.ec_sortref

  5. Multiple revisions to the GROUP BY reordering tests

  6. Get rid of pg_class usage in SJE regression tests

  7. Rename index "abc" in aggregates.sql

  8. Explore alternative orderings of group-by pathkeys during optimization.

  9. Generalize the common code of adding sort before processing of grouping

  10. Fix out-dated comment in preprocess_groupclause()

  11. Force parallelism in partition_aggregate

  12. Optimize order of GROUP BY keys

Alexander Korotkov <aekorotkov@gmail.com> writes:
> On Wed, Dec 27, 2023 at 5:23 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I think it's a fool's errand to even try to separate different sort
>> column orderings by cost.

> Besides sorting column orderings by cost, this patch also tries to
> match GROUP BY pathkeys to input pathkeys and ORDER BY pathkeys.  Do
> you think there is a chance for the second part if we leave the cost
> part aside?

I think it's definitely reasonable to try to match up available
orderings, because that doesn't really require fine distinctions
of cost: either it matches or it doesn't.  Eliminating a sort step
entirely is clearly a win.  (Incremental sort complicates this though.
I doubt our cost model for incremental sorts is any good either, so
I am not eager to rely on that more heavily.)

			regards, tom lane