Re: POC: GROUP BY optimization

From: Dmitry Dolgov <9erthalion6(at)gmail(dot)com>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: Teodor Sigaev <teodor(at)sigaev(dot)ru>, Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, Andres Freund <andres(at)anarazel(dot)de>, Michael Paquier <michael(at)paquier(dot)xyz>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: POC: GROUP BY optimization
Date: 2020-05-16 12:24:31
Message-ID: 20200516122431.b7wtpm7dspsaxfro@localhost
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> 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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