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help / color / mirror / Atom feedFrom: Andrey Lepikhov <[email protected]>
To: Tomas Vondra <[email protected]>
To: Teodor Sigaev <[email protected]>
Cc: Tomas Vondra <[email protected]>
Cc: PostgreSQL Developers <[email protected]>
Subject: Re: POC: GROUP BY optimization
Date: Mon, 24 Jan 2022 10:02:03 +0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <CA+q6zcVRrd-z4YZ4M43ccst7aGL9==w5r1fionRWhP9ot6mybQ@mail.gmail.com>
<20201026085721.g6h5xljxvodnmk34@localhost>
<CALT9ZEF8FUZoijXnFsDXNgqbSHFzaCU2q0cmJFnZ4z2wNZO98w@mail.gmail.com>
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<CALT9ZEEqnS+tObVjLWZrUme-PZQ-O0krpFCfQhwG-4ziSeSrBQ@mail.gmail.com>
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On 22/1/2022 01:34, Tomas Vondra wrote:
> The other thing we could do is reduce the coefficient gradually - so
> it'd be 1.5 for the first pathkey, then 1.25 for the next one, and so
> on. But it seems somewhat arbitrary (I certainly don't have some sound
> theoretical justification ...).
I think, it hasn't a reason to increase complexity without any theory at
the bottom. Simple solution allows to realize problems much faster, if
they arise.
> ... I've skipped the path_save
> removal in planner.c, because that seems incorrect - if there are
> multiple pathkeys, we must start with the original path, not the
> modified one we built in the last iteration. Or am I missing something
You are right, I misunderstood the idea of path_save variable.
--
regards,
Andrey Lepikhov
Postgres Professional
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