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From: Robert Haas <[email protected]>
To: Tom Lane <[email protected]>
Cc: 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: Fri, 26 Jan 2024 10:41:05 -0500
Message-ID: <CA+TgmoZHC=Lp83eucToAwNzoMeiaRMeTXqhPeGSquGLuGRgmTg@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
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On Fri, Jan 26, 2024 at 10:38 AM Tom Lane <[email protected]> wrote:
> Sadly, that's not a small task:
>
> * We'd need to put effort into assigning more realistic procost
> values --- preferably across the board, not just comparison functions.
> As long as all the comparison functions have procost 1.0, you're
> just flying blind.
>
> * As you mentioned, there'd need to be some accounting for the
> likely size of varlena inputs, and especially whether they might
> be toasted.
>
> * cost_sort knows nothing of the low-level sort algorithm improvements
> we've made in recent years, such as abbreviated keys.
>
> That's a lot of work, and I think it has to be done before we try
> to build infrastructure on top, not afterwards.

OK, that makes sense to me. Thanks.

-- 
Robert Haas
EDB: http://www.enterprisedb.com

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