From: Tom Lane <tgl@sss.pgh.pa.us>
To: Greg Smith <gsmith@gregsmith.com>
Cc: Guillaume Smet <guillaume.smet@gmail.com>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Cc: Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>
Cc: Devrim GÜNDÜZ <devrim@commandprompt.com>
Subject: Re: More shared buffers causes lower performances
Date: Thu, 27 Dec 2007 01:10:29 -0500
Message-ID: <29359.1198735829@sss.pgh.pa.us> (raw)
In-Reply-To: <Pine.GSO.4.64.0712261816520.16448@westnet.com>
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Greg Smith <gsmith@gregsmith.com> writes:
> On Wed, 26 Dec 2007, Guillaume Smet wrote:
>> beta RPMs are by default compiled with --enable-debug and
>> --enable-cassert which doesn't help them to fly fast...
> Got that right. Last time I was going crazy after running pgbench with
> those options and not having realized what I changed, I was getting a 50%
> slowdown on results that way compared to without the debugging stuff.
> Didn't realize it scaled with shared_buffers though.
See AtEOXact_Buffers(). There are probably any number of other
interesting scaling behaviors --- in my tests, AllocSetCheck() is
normally a major cycle-eater if --enable-cassert is set, and that costs
time proportional to the number of memory chunks allocated by the query.
Currently the docs say that --enable-cassert
Enables <firstterm>assertion</> checks in the server, which test for
many <quote>cannot happen</> conditions. This is invaluable for
code development purposes, but the tests slow things down a little.
Maybe we ought to put that more strongly --- s/a little/significantly/,
perhaps?
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, gsmith@gregsmith.com, guillaume.smet@gmail.com, stefan@kaltenbrunner.cc, devrim@commandprompt.com
Subject: Re: More shared buffers causes lower performances
In-Reply-To: <29359.1198735829@sss.pgh.pa.us>
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