From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
cc: "David G. Johnston" <david.g.johnston@gmail.com>,
        Stephen Frost <sfrost@snowman.net>, 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>,
        "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Default setting for enable_hashagg_disk
In-reply-to: <20200712003037.wzrcltujwzwiwlfr@development>
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Comments: In-reply-to Tomas Vondra <tomas.vondra@2ndquadrant.com>
	message dated "Sun, 12 Jul 2020 02:30:37 +0200"
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Date: Sat, 11 Jul 2020 20:47:54 -0400
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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