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From: Tom Lane <[email protected]>
To: Alexander Korotkov <[email protected]>
Cc: Andrei Lepikhov <[email protected]>
Cc: PostgreSQL Developers <[email protected]>
Cc: Tomas Vondra <[email protected]>
Cc: Teodor Sigaev <[email protected]>
Cc: David Rowley <[email protected]>
Cc: a.rybakina <[email protected]>
Cc: Белялов Дамир Наилевич <[email protected]>
Subject: Re: POC: GROUP BY optimization
Date: Tue, 26 Dec 2023 23:27:39 -0500
Message-ID: <[email protected]> (raw)
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Alexander Korotkov <[email protected]> writes:
> On Wed, Dec 27, 2023 at 5:23 AM Tom Lane <[email protected]> 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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