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From: Dmitry Dolgov <9erthalion6@gmail.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Teodor Sigaev <teodor@sigaev.ru>
Cc: Gavin Flower <GavinFlower@archidevsys.co.nz>
Cc: Andres Freund <andres@anarazel.de>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Subject: Re: POC: GROUP BY optimization
Date: Sat, 16 May 2020 14:24:31 +0200
Message-ID: <20200516122431.b7wtpm7dspsaxfro@localhost> (raw)
In-Reply-To: <20200514235220.xewrrwjvatxzn3g6@development>
References: <20181002021626.GF11712@paquier.xyz>
	<CA+q6zcVFEB--p=e2S-mY6UB87YCBBh=5WXdw2Gqr-2nBGtLkjg@mail.gmail.com>
	<20190131112407.zpbysdvghjyh4z47@alap3.anarazel.de>
	<CA+q6zcVfsx_YuETPmjkNq-1=kJCS5JuShrL2ZNzm_HRVZ-tiYg@mail.gmail.com>
	<20190409152100.5q25whnxs27zws5m@development>
	<CA+q6zcVRrd-z4YZ4M43ccst7aGL9==w5r1fionRWhP9ot6mybQ@mail.gmail.com>
	<20190503215510.bcr5ycszntqg65tw@development>
	<CA+q6zcVjCVkAhoLD6rjDoPGdfWDjQLD=N2tvfH1yU+Eq+iby9w@mail.gmail.com>
	<20190524225725.embuha33qvc5avz3@development>
	<20200514235220.xewrrwjvatxzn3g6@development>

> On Fri, May 15, 2020 at 01:52:20AM +0200, Tomas Vondra wrote:
>
> I wonder if anyone has plans to try again with this optimization in v14
> cycle? The patches no longer apply thanks to the incremental sort patch,
> but I suppose fixing that should not be extremely hard.
>
> The 2020-07 CF is still a couple weeks away, but it'd be good to know if
> there are any plans to revive this. I'm willing to spend some time on
> reviewing / testing this, etc.

Yes, if you believe that this patch has potential, I would love to pick
it up again.

> I've only quickly skimmed the old thread, but IIRC there were two main
> challenges in getting the optimization right:
>
>
> 1) deciding which orderings are interesting / worth additional work
>
> I think we need to consider these orderings, in addition to the one
> specified in GROUP BY:
>
> 1) as specified in ORDER BY (if different from 1)

What is the idea behind considering this ordering?





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  Cc: 9erthalion6@gmail.com, tomas.vondra@2ndquadrant.com, teodor@sigaev.ru, GavinFlower@archidevsys.co.nz, andres@anarazel.de, michael@paquier.xyz, pgsql-hackers@lists.postgresql.org
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