Re: PG15 beta1 sort performance regression due to Generation context change

From: "Jonathan S(dot) Katz" <jkatz(at)postgresql(dot)org>
To: David Rowley <dgrowleyml(at)gmail(dot)com>, John Naylor <john(dot)naylor(at)enterprisedb(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, Andres Freund <andres(at)anarazel(dot)de>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Michael Paquier <michael(at)paquier(dot)xyz>
Subject: Re: PG15 beta1 sort performance regression due to Generation context change
Date: 2022-07-13 13:23:00
Message-ID: fa16f10f-e814-31ca-bf67-93529e982438@postgresql.org
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Hi David,

On 7/13/22 12:13 AM, David Rowley wrote:
> On Tue, 12 Jul 2022 at 17:15, David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
>> So far only Robert has raised concerns with this regression for PG15
>> (see [2]). Tom voted for leaving things as they are for PG15 in [3].
>> John agrees, as quoted above. Does anyone else have any opinion?
>
> Let me handle this slightly differently. I've moved the open item for
> this into the "won't fix" section. If nobody shouts at me for that
> then I'll let that end the debate. Otherwise, we can consider the
> argument when it arrives.

The RMT discussed this issue at its meeting today (and a few weeks back
-- apologies for not writing sooner). While we agree with your analysis
that 1/ this issue does appear to be a corner case and 2/ the benefits
outweigh the risks, we still don't know how prevalent it may be in the
wild and the general impact to user experience.

The RMT suggests that you make one more pass at attempting to solve it.
If there does not appear to be a clear path forward, we should at least
document how a user can detect and resolve the issue.

Thanks,

Jonathan

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