On Tue, 25 Nov 2014 16:43:49 +0100
Maila Fatticcioni <mfatticcioni@mbigroup.it> wrote:
> Hello,
> I need to install a Postgresql 9.4 cluster with two servers at first
> instance. The database will be used in an enviroment with high load, a
> lot number of clients will do queries that require fast replies.
> I have to install Ubuntu 14.04 as OS and I would like to know which
> filesystem you would suggest me to use. I have read that ZFS with ZIL
> is now mature for a production server: do you think it is that true or
> that it would be better to stay safer with a common EXT4?
We did a lot of research into this at my last employer. Unfortunatley, I
don't remember most of it, but I'll relay what I do remember.
Anything with a journal is a performance problem. PostgreSQL effectivly
does its own journalling with the WAL logs. That's not to say that there's
no value to crash recovery to having a journalling filesystem, but it's
just to say that our experience showed journaling filesystems to be slower.
That rules out ext4, unless you disable the journal. I seem to remember
ext4 with journalling disabled being one of the faster filesystems, but I
could be remembering wrong.
At the time we tested it, ZFS performance was terrible for databases. ZFS
continues to evolve, so that information might not be accurate any more.
Now ... if I remember correctly, we decided that XFS was the fastest of the
ones we tested. If I'm remembering correctly, the performance of XFS was
only a little bit better than ext4 with journalling disabled and there was
considerable debate as to whether it was worth going with something less
widely used and supported (XFS) to gain only a tiny % of improvement over
something heavily used and tested (ext4). Sorry I can't be more definite, but
I don't have access to the information any more.
On a related note, I remember that the sysops guys had a list of mount options
that they used to improve performance ... noatime being one that I remember,
but whatever filesystem you use, be sure to research and tweak the mount
options.
--
Bill Moran
I need your help to succeed:
http://gamesbybill.com
