From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: "Fujii.Yuki@df.MitsubishiElectric.co.jp" <Fujii.Yuki@df.mitsubishielectric.co.jp>,
        Alexander Pyhalov <a.pyhalov@postgrespro.ru>,
        Bruce Momjian <bruce@momjian.us>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>,
        "Finnerty,
    Jim" <jfinnert@amazon.com>,
        Andres Freund <andres@anarazel.de>,
        Tomas Vondra <tomas.vondra@enterprisedb.com>,
        Julien Rouhaud <rjuju123@gmail.com>,
        Daniel Gustafsson <daniel@yesql.se>
Subject: Re: Partial aggregates pushdown
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References: <TYTPR01MB1095486F5E3103D783AF4748995DFA@TYTPR01MB10954.jpnprd01.prod.outlook.com> <ZTmR1wIr2_A-vw33@momjian.us> <TYTPR01MB10954D890D8F729E1BCE42D4F95DDA@TYTPR01MB10954.jpnprd01.prod.outlook.com> <ZTrBYS71CrnnA7xa@momjian.us> <TYTPR01MB10954B4C9A791FA9D2BF692F095DCA@TYTPR01MB10954.jpnprd01.prod.outlook.com> <ZTspKdU1sZ4qKLD8@momjian.us> <TYTPR01MB10954B96601911FE868BF88E895DCA@TYTPR01MB10954.jpnprd01.prod.outlook.com> <OSZPR01MB9424BB7E885791D88B80F7B395B3A@OSZPR01MB9424.jpnprd01.prod.outlook.com> <OSZPR01MB94244C52ABBE67C4A033B5E495B3A@OSZPR01MB9424.jpnprd01.prod.outlook.com> <CA+Tgmobvja+jytj5zcEcYgqzOaeJiqrrJxgqDf1q=3k8FepuWQ@mail.gmail.com> <ZVviSttXc7kff_I5@momjian.us> <CA+TgmoaiH_Na3y17PankZH59EgJWbgdPM-szb1eP6DQoOAMgYg@mail.gmail.com> <8175ddeb6d417d8a1f91e667fef77abf@postgrespro.ru> <TYAPR01MB55149B8569F2FDA262654C4F95BAA@TYAPR01MB5514.jpnprd01.prod.outlook.com> <CA+TgmoYQKF-8vL8sctWuw_dskBiQWcspuNPJuH4ttusuiP529g@mail.gmail.com> <4010199.1701118769@sss.p!
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Mon, 27 Nov 2023 16:10:02 -0500"
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Date: Mon, 27 Nov 2023 16:23:24 -0500
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Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, Nov 27, 2023 at 3:59 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> TBH, I think this entire proposal is dead in the water.  Which is
>> sad from a performance standpoint, but I can't see any way that
>> we would not regret shipping a feature that makes such assumptions.

> I think it's ridiculous to just hold our breath and pretend like this
> feature isn't needed -- it's at least half a decade overdue. We engage
> in endless hand-wringing over local-remote symmetry in cases where
> other systems seem to effortlessly make that assumption and then get
> on with building new features.

Well, one of the founding principles of postgres_fdw was to be able
to talk to PG servers that are not of the same version as yours.
If we break that in the name of performance, we are going to have
a lot of unhappy users.  Even the ones who do get the benefit of
the speedup are going to be unhappy when it breaks because they
didn't upgrade local and remote at exactly the same time.

Just because we'd like to have it doesn't make the patch workable
in the real world.

			regards, tom lane