From: Joris Dobbelsteen <joris@familiedobbelsteen.nl>
To: Matthew Pulis <mpulis@gmail.com>
Cc: pgsql-admin@postgresql.org
Cc: pgsql-general@postgresql.org
Subject: Re: [GENERAL] PostgreSQL Cache
Date: Mon, 29 Sep 2008 09:01:12 +0200
Message-ID: <48E07D38.90906@familiedobbelsteen.nl> (raw)
In-Reply-To: <f88da7150809282143w71c0920avb51f7809eb398ef7@mail.gmail.com>
References: <f88da7150809282143w71c0920avb51f7809eb398ef7@mail.gmail.com>
Matthew Pulis wrote:
> Hi,
>
> I need to perform some timed testing, thus need to make sure that disk
> cache does not affect me. Is clearing the OS (Ubuntu) disk cache, ( by
> running: sudo echo 3 | sudo tee /proc/sys/vm/drop_caches ) enough to
> do this? If not can you please point me to some site please since all
> I am finding is such command.
Look for methodologies for doing performance tests. A problem is that
the disk cache is an essential part that makes up for postgresql
performance. Also do not forget about overhead and inaccuracies that you
will affect your results.
In general performance tests are a rather large simulation of how your
application would use the database. It should be large enough for many
effects (such as initial cache state) to be neglected. It only provides
an average for the performance on your system configuration.
If you run it a few times more, you can compute the variation. It
provides some insight how stable your system is in handling the workload.
- Joris
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To: pgsql-admin@postgresql.org
Cc: joris@familiedobbelsteen.nl, mpulis@gmail.com, pgsql-general@postgresql.org
Subject: Re: [GENERAL] PostgreSQL Cache
In-Reply-To: <48E07D38.90906@familiedobbelsteen.nl>
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