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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jeff Davis <pgsql@j-davis.com>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: David Rowley <dgrowleyml@gmail.com>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: Andres Freund <andres@anarazel.de>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Robert Haas <robertmhaas@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: Mon, 20 Jul 2020 19:25:39 +0200
Message-ID: <20200720172539.6jov6ynljly4wj6i@development> (raw)
In-Reply-To: <400617.1595251041@sss.pgh.pa.us>
References: <CAH2-WzmaJG4QYHq5LR+ZXEf1JMVcTzT9pEOeMFg0uuGXYDvgzQ@mail.gmail.com>
	<9e4a4cffe3eee0543e5b94c90821d39e03b81d29.camel@j-davis.com>
	<CAH2-Wz=qBF1QyXKdB6YNV993WpQ0wj-x4h8r9yjYUwQRCMkLjA@mail.gmail.com>
	<6d0aba397625df79bdc3ca85adc11b9e48ecb0da.camel@j-davis.com>
	<4118680.1595097043@sss.pgh.pa.us>
	<571473265c5d5309f4012855ebd2131c136073ab.camel@j-davis.com>
	<32871.1595121333@sss.pgh.pa.us>
	<88c0af01ad9ac105e424768808a214d855e29a77.camel@j-davis.com>
	<20200720004827.4c46ikcdrfum6xyu@development>
	<400617.1595251041@sss.pgh.pa.us>

On Mon, Jul 20, 2020 at 09:17:21AM -0400, Tom Lane wrote:
>Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
>> There's a minor problem here, though - these stats were collected before
>> we fixed the tlist issue, so hashagg was spilling about 10x the amount
>> of data compared to sort+groupagg. So maybe that's the first thing we
>> should do, before contemplating changes to the costing - collecting
>> fresh data. I can do that, if needed.
>
>+1.  I'm not sure if we still need to do anything, but we definitely
>can't tell on the basis of data that doesn't reliably reflect what
>the code does now.
>

OK, will do. The hardware is busy doing something else at the moment,
but I'll do the tests and report results in a couple days.


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services 

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