Re: PostgreSQL with ZFS on Linux

On 16 January 2014 12:09, Achilleas Mantzios
<achill(at)matrix(dot)gatewaynet(dot)com> wrote:
> http://www.unix-experience.fr/2013/2451/
>
> FreeBSD is also a very mature platform for ZFS/postgresql.

More mature than on Linux even, as far as I know. If I had to choose
an OS to use ZFS with, I'd go with
either FreeBSD or Solaris. That said, I am biased to FreeBSD anyway;
the only Linux installation that I
own is the one in my Android phone, while I own several FreeBSD systems.

> On Thu, Jan 16, 2014 at 4:22 AM, Sébastien Lorion <sl(at)thestrangefactory(dot)com>
> wrote:
>>
>> Hello,
>>
>> Since ZFS on Linux (http://zfsonlinux.org/) has been declared production
>> ready last March (v0.6.1), I am curious if anyone is using it with
>> PostgreSQL on production servers (either main or backup) and if so, what is
>> their experience so far ?
>>
>> Thank you,
>>
>> Sébastien

I do not consider ZFS an ideal file-system for databases. I'm not an
expert on ZFS, but there are two
features in ZFS that I think particularly make it less suitable for
database use.

One reason is that ZFS, as I understand it, is a log-structured
file-system. That means that changes to files always
go to the end of the file-system. If that file is a large frequently
updated database table, records are going to be far
apart and in fairly random order. That could seriously hurt performance.

Secondly, with ZFS you need to reserve a significant amount of memory
for the ZIL. That is memory that is
not available to your database.

Don't take my word for it, but I think the above points are worth
investigating as is finding some file-system bench-
marks where ZFS gets compared to, for example, UFS2 (FreeBSD), Ext4fs (Linux).
Of course, the other side of the coin is ZFS's excellent flexibility.

Cheers,

Alban Hertroys
--
If you can't see the forest for the trees,
Cut the trees and you'll see there is no forest.