From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: David G. Johnston <david.g.johnston@gmail.com>
Cc: 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: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: Default setting for enable_hashagg_disk
Date: Sun, 12 Jul 2020 14:30:43 +0200
Message-ID: <20200712123043.hnjsluya5mbwhnq4@development> (raw)
In-Reply-To: <2463591.1594514874@sss.pgh.pa.us>
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<20200710141714.GI12375@tamriel.snowman.net>
<CAH2-Wzkd7cWK-mMPMb63JXxj2QFMan6hw+cQjdJKvdtCOpR7Ng@mail.gmail.com>
<20200710215012.GN12375@tamriel.snowman.net>
<2165606.1594418399@sss.pgh.pa.us>
<20200711142213.GP12375@tamriel.snowman.net>
<CAKFQuwY8dVgkMgQb4BCEqrp8CVZx6p1AjFB773XNqrQnSHAvuw@mail.gmail.com>
<20200712003037.wzrcltujwzwiwlfr@development>
<2463591.1594514874@sss.pgh.pa.us>
On Sat, Jul 11, 2020 at 08:47:54PM -0400, Tom Lane wrote:
>Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
>> I don't know, but one of the main arguments against simply suggesting
>> people to bump up work_mem (if they're hit by the hashagg spill in v13)
>> was that it'd increase overall memory usage for them. It seems strange
>> to then propose a new GUC set to a default that would result in higher
>> memory usage *for everyone*.
>
>It seems like a lot of the disagreement here is focused on Peter's
>proposal to make hash_mem_multiplier default to 2.0. But it doesn't
>seem to me that that's a critical element of the proposal. Why not just
>make it default to 1.0, thus keeping the default behavior identical
>to what it is now?
>
>If we find that's a poor default, we can always change it later;
>but it seems to me that the evidence for a higher default is
>a bit thin at this point.
>
You're right, I was specifically pushing against that aspect of the
proposal. Sorry for not making that clearer, I assumed it's clear from
the context of this (sub)thread.
I agree making it 1.0 (or equal to work_mem, if it's not a multiplier)
by default, but allowing it to be increased if needed would address most
of the spilling issues.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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To: pgsql-hackers@postgresql.org
Cc: tomas.vondra@2ndquadrant.com, tgl@sss.pgh.pa.us, david.g.johnston@gmail.com, 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
Subject: Re: Default setting for enable_hashagg_disk
In-Reply-To: <20200712123043.hnjsluya5mbwhnq4@development>
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