From: Greg Smith <greg@2ndquadrant.com>
To: Josh Berkus <josh@agliodbs.com>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: pgsql-performance@postgresql.org, Albe Laurenz <laurenz.albe@wien.gv.at>
Subject: Re: Linux I/O tuning: CFQ vs. deadline
Date: Mon, 08 Feb 2010 23:14:15 -0500
Message-ID: <4B70E117.6070708@2ndquadrant.com> (raw)
In-Reply-To: <4B704EA0.3050906@agliodbs.com>
References: <4B6FDD26.9010106@2ndquadrant.com>
<D960CB61B694CF459DCFB4B0128514C203938157@exadv11.host.magwien.gv.at>
<4B6FD868020000250002F084@gw.wicourts.gov>
<4B702E05.1000708@2ndquadrant.com>
<4B704EA0.3050906@agliodbs.com>
Josh Berkus wrote:
> FWIW, back when deadline was first introduced Mark Wong did some tests
> and found Deadline to be the fastest of 4 on DBT2 ... but only by about
> 5%. If the read vs. checkpoint analysis is correct, what was happening
> is the penalty for checkpoints on deadline was almost wiping out the
> advantage for reads, but not quite.
>
Wasn't that before 8.3, where the whole checkpoint spreading logic
showed up? That's really a whole different write pattern now than it
was then. 8.2 checkpoint writes were one big batch write amenable to
optimizing for throughput. The new ones are not; the I/O is intermixed
with reads most of the time.
> Man, we'd need a lot of testing to settle this. I guess that's why
> Linux gives us the choice of 4 ...
>
A recent on of these I worked on started with 4096 possible I/O
configurations we pruned down the most likely good candidates from. I'm
almost ready to schedule a week on Mark's HP performance test system in
the lab now, to try and nail this down in a fully public environment for
once.
--
Greg Smith 2ndQuadrant Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com www.2ndQuadrant.com
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To: pgsql-performance@postgresql.org
Cc: greg@2ndquadrant.com, josh@agliodbs.com, Kevin.Grittner@wicourts.gov, laurenz.albe@wien.gv.at
Subject: Re: Linux I/O tuning: CFQ vs. deadline
In-Reply-To: <4B70E117.6070708@2ndquadrant.com>
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