From: Tom Lane <tgl@sss.pgh.pa.us>
To: Stephen Frost <sfrost@snowman.net>
cc: Peter Geoghegan <pg@bowt.ie>, Jeff Davis <pgsql@j-davis.com>,
        Alvaro Herrera <alvherre@2ndquadrant.com>,
        Andres Freund <andres@anarazel.de>, Bruce Momjian <bruce@momjian.us>,
        Robert Haas <robertmhaas@gmail.com>,
        David Rowley <dgrowleyml@gmail.com>,
        Justin Pryzby <pryzby@telsasoft.com>,
        Melanie Plageman <melanieplageman@gmail.com>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Default setting for enable_hashagg_disk
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Comments: In-reply-to Stephen Frost <sfrost@snowman.net>
	message dated "Fri, 10 Jul 2020 17:50:13 -0400"
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Date: Fri, 10 Jul 2020 17:59:59 -0400
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Stephen Frost <sfrost@snowman.net> writes:
> I don't see hash_mem as being any kind of proper fix- it's just punting
> to the user saying "we can't figure this out, how about you do it" and,
> worse, it's in conflict with how we already ask the user that question.
> Turning it into a multiplier doesn't change that either.

Have you got a better proposal that is reasonably implementable for v13?
(I do not accept the argument that "do nothing" is a better proposal.)

I agree that hash_mem is a stopgap, whether it's a multiplier or no,
but at this point it seems difficult to avoid inventing a stopgap.
Getting rid of the process-global work_mem setting is a research project,
and one I wouldn't even count on having results from for v14.  In the
meantime, it seems dead certain that there are applications for which
the current behavior will be problematic.  hash_mem seems like a cleaner
and more useful stopgap than the "escape hatch" approach, at least to me.

			regards, tom lane