From: Kevin Grittner <Kevin.Grittner@wicourts.gov>
To: Greg Smith *EXTERN* <greg@2ndquadrant.com>
To: pgsql-performance@postgresql.org
To: Albe Laurenz <laurenz.albe@wien.gv.at>
Subject: Re: Linux I/O tuning: CFQ vs. deadline
Date: Mon, 08 Feb 2010 09:24:56 -0600
Message-ID: <4B6FD868020000250002F084@gw.wicourts.gov> (raw)
In-Reply-To: <D960CB61B694CF459DCFB4B0128514C203938157@exadv11.host.magwien.gv.at>
References: <4B6FDD26.9010106@2ndquadrant.com>
<D960CB61B694CF459DCFB4B0128514C203938157@exadv11.host.magwien.gv.at>
"Albe Laurenz" <laurenz.albe@wien.gv.at> wrote:
> Greg Smith wrote:
>> http://insights.oetiker.ch/linux/fsopbench/
>
> That is interesting; particularly since I have made one quite
> different experience in which deadline outperformed CFQ by a
> factor of approximately 4.
I haven't benchmarked it per se, but when we started using
PostgreSQL on Linux, the benchmarks and posts I could find
recommended deadline=elevator, so we went with that, and when the
setting was missed on a machine it was generally found fairly
quickly because people complained that the machine wasn't performing
to expectations; changing this to deadline corrected the problem.
> So I tried to look for differences, and I found two possible
> places:
> - My test case was read-only, our production system is
> read-mostly.
Yeah, our reads are typically several times our writes -- up to
maybe 10 to 1.
> - We did not have a RAID array, but a SAN box (with RAID inside).
No SAN here, but if I recall correctly, this was mostly an issue on
our larger arrays -- RAID 5 with dozens of spindles on a BBU
hardware controller.
Other differences between our environment and that of the benchmarks
cited above:
- We use SuSE Linux Enterprise Server, so we've been on *much*
earlier kernel versions that this benchmark.
- We've been using xfs, with noatime,nobarrier.
I'll keep this in mind as something to try if we have problem
performance in line with what that page describes, though....
-Kevin
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To: pgsql-performance@postgresql.org
Cc: Kevin.Grittner@wicourts.gov, greg@2ndquadrant.com, laurenz.albe@wien.gv.at
Subject: Re: Linux I/O tuning: CFQ vs. deadline
In-Reply-To: <4B6FD868020000250002F084@gw.wicourts.gov>
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