| From: | Alexander Korotkov <aekorotkov(at)gmail(dot)com> |
|---|---|
| To: | Andrei Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Teodor Sigaev <teodor(at)sigaev(dot)ru>, David Rowley <dgrowleyml(at)gmail(dot)com>, "a(dot)rybakina" <a(dot)rybakina(at)postgrespro(dot)ru>, Белялов Дамир Наилевич <d(dot)belyalov(at)postgrespro(dot)ru> |
| Subject: | Re: POC: GROUP BY optimization |
| Date: | 2023-12-28 11:29:05 |
| Message-ID: | CAPpHfdvnpQ_78_bW8TQU_j64haz9WGOYS3Zx=5tw70ge7c_eWA@mail.gmail.com |
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On Thu, Dec 28, 2023 at 10:22 AM Andrei Lepikhov
<a(dot)lepikhov(at)postgrespro(dot)ru> wrote:
> But arrangement with an ORDER BY clause doesn't work:
>
> DROP INDEX abc;
> explain SELECT x,w,z FROM t GROUP BY (w,x,z) ORDER BY (x,z,w);
>
> I think the reason is that the sort_pathkeys and group_pathkeys are
> physically different structures, and we can't just compare pointers here.
I haven't yet looked into the code. But this looks strange to me.
Somehow, optimizer currently matches index pathkeys to ORDER BY
pathkeys. If GROUP BY pathkeys could be matched to index pathkeys,
then it should be possible to match them to ORDER BY pathkeys too.
------
Regards,
Alexander Korotkov
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