From: Scott Carey <scott@richrelevance.com>
To: Greg Smith <gsmith@gregsmith.com>
CC: Josh Berkus <josh@agliodbs.com>, henk de wit <henk53602@hotmail.com>,
	"jesper@krogh.cc" <jesper@krogh.cc>, "pgsql-performance@postgresql.org"
	<pgsql-performance@postgresql.org>
Date: Fri, 10 Apr 2009 11:17:39 -0700
Subject: Re: Using IOZone to simulate DB access patterns
Thread-Topic: [PERFORM] Using IOZone to simulate DB access patterns
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On 4/10/09 11:01 AM, "Greg Smith" <gsmith@gregsmith.com> wrote:

> On Fri, 10 Apr 2009, Scott Carey wrote:
>=20
>> FIO with profiles such as the below samples are easy to set up
>=20
> There are some more sample FIO profiles with results from various
> filesystems at
> http://wiki.postgresql.org/wiki/HP_ProLiant_DL380_G5_Tuning_Guide

I wish to thank Greg here as many of my profile variations came from the
above as a starting point.

Note in his results the XFS file system behavior on random writes is due to
FIO doing 'sparse writes' (which Postgres does not do, and fio exposes some
issues on xfs with) in the default random write mode.  To properly simulate
Postgres these should be random overwrites.

Add 'overwrite=3Dtrue' to the profile for random writes and the whole file
will be allocated before randomly (over)writing to it.

Here is the man page:
http://linux.die.net/man/1/fio

>=20
> --
> * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD
>=20