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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
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: Sat, 11 Jul 2020 20:47:54 -0400
Message-ID: <2463591.1594514874@sss.pgh.pa.us> (raw)
In-Reply-To: <20200712003037.wzrcltujwzwiwlfr@development>
References: <20200709225840.GE12375@tamriel.snowman.net>
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<20200712003037.wzrcltujwzwiwlfr@development>
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.
regards, tom lane
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