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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 22:23:24 -0500
Message-ID: <[email protected]> (raw)
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Alexander Korotkov <[email protected]> writes:
> 2) An accurate estimate of the sorting cost is quite a difficult task.

Indeed.

> What if we make a simple rule of thumb that sorting integers and
> floats is cheaper than sorting numerics and strings with collation C,
> in turn, that is cheaper than sorting collation-aware strings
> (probably more groups)?  Within the group, we could keep the original
> order of items.

I think it's a fool's errand to even try to separate different sort
column orderings by cost.  We simply do not have sufficiently accurate
cost information.  The previous patch in this thread got reverted because
of that (well, also some implementation issues, but mostly that), and
nothing has happened to make me think that another try will fare any
better.

			regards, tom lane






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