Horton

Re: POC: GROUP BY optimization

Andrei Lepikhov <a.lepikhov@postgrespro.ru>

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From: Andrei Lepikhov <a.lepikhov@postgrespro.ru>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Pavel Borisov <pashkin.elfe@gmail.com>, vignesh C <vignesh21@gmail.com>, 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>, Tom Lane <tgl@sss.pgh.pa.us>
Date: 2024-01-14T12:14:13Z
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. 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

Attachments

On 13/1/2024 22:00, Alexander Korotkov wrote:
> On Sat, Jan 13, 2024 at 11:09 AM Andrei Lepikhov
> <a.lepikhov@postgrespro.ru> wrote:
>> On 11/1/2024 18:30, Alexander Korotkov wrote:
>>> On Tue, Jan 9, 2024 at 1:14 PM Pavel Borisov <pashkin.elfe@gmail.com> wrote:
>>>>> Hmm, I don't see this old code in these patches. Resend 0002-* because
>>>>> of trailing spaces.
>>>>
>>>>
>>>> AFAIK, cfbot does not seek old versions of patchset parts in previous messages. So for it to run correctly, a new version of the whole patchset should be sent even if most patches are unchanged.
>>>
>>> Please, find the revised patchset with some refactoring and comments
>>> improvement from me.  I'll continue looking into this.
>> The patch looks better, thanks to your refactoring.
>> I propose additional comments and tests to make the code more
>> understandable (see attachment).
>> I intended to look into this part of the code more, but the tests show a
>> difference between PostgreSQL v.15 and v.16, which causes changes in the
>> code of this feature.
> 
> Makes sense.  I've incorporated your changes into the patchset.
One more improvement. To underpin code change:

-               return cur_ec;  /* Match! */
+           {
+               /*
+                * Match!
+                *
+                * Copy the sortref if it wasn't set yet. That may happen if
+                * the ec was constructed from WHERE clause, i.e. it doesn't
+                * have a target reference at all.
+                */
+               if (cur_ec->ec_sortref == 0 && sortref > 0)
+                   cur_ec->ec_sortref = sortref;
+               return cur_ec;
+           }

I propose the test (see attachment). It shows why we introduce this 
change: GROUP-BY should juggle not only pathkeys generated by explicit 
sort operators but also planner-made, likewise in this example, by 
MergeJoin.

-- 
regards,
Andrei Lepikhov
Postgres Professional