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From: Robert Haas <robertmhaas@gmail.com>
Date: Thu, 29 Aug 2024 08:40:09 -0400
Message-ID: <CA+TgmoYdO68GtU9WZ1_a+gJs7fZ96sNraxyvVwu4iRYv4kYmLQ@mail.gmail.com>
Subject: Re: Eager aggregation, take 3
To: Richard Guo <guofenglinux@gmail.com>
Cc: Paul George <p.a.george19@gmail.com>, Andy Fan <zhihuifan1213@163.com>, 
	PostgreSQL-development <pgsql-hackers@postgresql.org>, pgsql-hackers@lists.postgresql.org
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On Wed, Aug 28, 2024 at 10:26=E2=80=AFPM Richard Guo <guofenglinux@gmail.co=
m> wrote:
> Yeah, I'm concerned about this too.  In addition to the inaccuracies
> in aggregation estimates, our estimates for joins are sometimes not
> very accurate either.  All this are likely to result in regressions
> with eager aggregation in some cases.  Currently I don't have a good
> answer to this problem.  Maybe we can run some benchmarks first and
> investigate the regressions discovered on a case-by-case basis to better
> understand the specific issues.

While it's true that we can make mistakes during join estimation, I
believe aggregate estimation tends to be far worse.

--=20
Robert Haas
EDB: http://www.enterprisedb.com