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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Stephen Frost <sfrost@snowman.net>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: Jeff Davis <pgsql@j-davis.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: David Rowley <dgrowleyml@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>
Cc: Melanie Plageman <melanieplageman@gmail.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: Default setting for enable_hashagg_disk
Date: Fri, 10 Jul 2020 17:59:59 -0400
Message-ID: <2165606.1594418399@sss.pgh.pa.us> (raw)
In-Reply-To: <20200710215012.GN12375@tamriel.snowman.net>
References: <20200708140037.GI3125@tamriel.snowman.net>
	<99b047386525b87df1e611335c2e57a6cdef346b.camel@j-davis.com>
	<20200709140330.GO3125@tamriel.snowman.net>
	<CAH2-WzmB04dxgRgjDGvDbugEFfHxMi2pyuJqsYr30x1RAEqSXg@mail.gmail.com>
	<20200709225840.GE12375@tamriel.snowman.net>
	<CAH2-WzmbycnZnxFTYnwkSkCPTVQbRoLiuEvo8gkZCKiQTL8GAQ@mail.gmail.com>
	<20200710000842.GF12375@tamriel.snowman.net>
	<CAH2-Wz=9f-gxPmqL9Lak0xddPmH0bgfAEioK+2BwTkuzyrtZEQ@mail.gmail.com>
	<20200710141714.GI12375@tamriel.snowman.net>
	<CAH2-Wzkd7cWK-mMPMb63JXxj2QFMan6hw+cQjdJKvdtCOpR7Ng@mail.gmail.com>
	<20200710215012.GN12375@tamriel.snowman.net>

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





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  Cc: tgl@sss.pgh.pa.us, sfrost@snowman.net, pg@bowt.ie, pgsql@j-davis.com, alvherre@2ndquadrant.com, andres@anarazel.de, bruce@momjian.us, robertmhaas@gmail.com, dgrowleyml@gmail.com, pryzby@telsasoft.com, melanieplageman@gmail.com, tomas.vondra@2ndquadrant.com
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