| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alexander Korotkov <aekorotkov(at)gmail(dot)com> |
| Cc: | Andrei Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru>, 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: | 2023-12-27 04:27:39 |
| Message-ID: | 2422164.1703651259@sss.pgh.pa.us |
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Alexander Korotkov <aekorotkov(at)gmail(dot)com> writes:
> On Wed, Dec 27, 2023 at 5:23 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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
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