From: Magnus Hagander <magnus@hagander.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: 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 09:47:59 +0100
Message-ID: <20071227084759.GB23218@svr2.hagander.net> (raw)
In-Reply-To: <29359.1198735829@sss.pgh.pa.us>
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<1d4e0c10712260741w1f141fd6x2f482143d526ad48@mail.gmail.com>
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<1d4e0c10712261352j2fbcd25ek1270331468d824b4@mail.gmail.com>
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<29359.1198735829@sss.pgh.pa.us>
On Thu, Dec 27, 2007 at 01:10:29AM -0500, Tom Lane wrote:
> 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?
Sounds like a good idea. We got bit by the same thing when doing some
benchmarks on the MSVC port (and with we I mean Dave did the work, and several
people couldn't understand why the numbers sucked)
//Magnus
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To: pgsql-performance@postgresql.org
Cc: magnus@hagander.net, 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: <20071227084759.GB23218@svr2.hagander.net>
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