From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: Jeff Davis <pgsql@j-davis.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 17:28:15 -0400
Message-ID: <2164047.1594416495@sss.pgh.pa.us> (raw)
In-Reply-To: <20200710211026.GA4375@alvherre.pgsql>
References: <20200710211026.GA4375@alvherre.pgsql>
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> On 2020-Jul-10, Peter Geoghegan wrote:
>> * The maximum allowable value is 100.0, to protect users from
>> accidentally setting hash_mem_multiplier to a value intended to work
>> like a work_mem-style KB value (you can't provide an absolute value
>> like that directly). This maximum is absurdly high.
> I'm not sure about this bit; sounds a bit like what has been qualified
> as "nannyism" elsewhere. Suppose I want to give a hash table 2GB of
> memory for whatever reason. If my work_mem is default (4MB) then I
> cannot possibly achieve that without altering both settings.
> So I propose that maybe we do want a maximum value, but if so it should
> be higher than what you propose. I think 10000 is acceptable in that it
> doesn't get in the way.
I was kind of thinking 1000 as the limit ;-). In any case, the code
will need to internally clamp the product to not exceed whatever the
work_mem physical limit is these days.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, alvherre@2ndquadrant.com, pg@bowt.ie, sfrost@snowman.net, pgsql@j-davis.com, andres@anarazel.de, bruce@momjian.us, robertmhaas@gmail.com, dgrowleyml@gmail.com, pryzby@telsasoft.com, melanieplageman@gmail.com, tomas.vondra@2ndquadrant.com
Subject: Re: Default setting for enable_hashagg_disk
In-Reply-To: <2164047.1594416495@sss.pgh.pa.us>
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