After a long battle with technology, "Pete de Zwart" <[EMAIL PROTECTED]>, an
earthling, wrote:
> Greetings to one and all,
>
> I've been trying to find some information on selecting an optimal
> filesystem setup for a volume that will only contain a PostgreSQL Database
> Cluster under Linux. Searching through the mailing list archive showed some
> promising statistics on the various filesystems available to Linux, ranging
> from ext2 through reiserfs and xfs.
>
> I have come to understand that PostgreSQLs Write Ahead Logging
> (WAL) performs a lot of the journal functionality provided by the
> majoirty of contemporary filesystems and that having both WAL and
> filesystem journalling can degrade performance.
>
> Could anyone point me in the right direction so that I can read
> up some more on this issue to discern which filesystem to choose and
> how to tune both the FS and PostgreSQL so that they can compliment
> each other? I've attempted to find this information via the FAQ,
> Google and the mailing list archives but have lucked out for the
> moment.
Your understanding of the impact of filesystem journalling isn't
entirely correct. In the cases of interest, journalling is done on
metadata, not on the contents of files, with the result that there
isn't really that much overlap between the two forms of "journalling"
that are taking place.
I did some benchmarking last year that compared, on a write-heavy
load, ext3, XFS, and JFS.
I found that ext3 was materially (if memory serves, 15%) slower than
the others, and that there was a persistent _slight_ (a couple
percent) advantage to JFS over XFS.
This _isn't_ highly material, particularly considering that I was
working with a 100% Write load, whereas "real world" work is likely to
have more of a mixture.
If you have reason to consider one filesystem or another better
supported by your distribution vendor, THAT is a much more important
reason to pick a particular filesystem than 'raw speed.'
--
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