Re: Postgresql on file system EXT2 or EXT3

On Fri, 2003-11-28 at 10:40, Christopher Browne wrote:
> miki@canaan.co.il ("Ben-Nes Michael") writes:
> > Don't go on EXT2, its not reliable and takes lots of time to start after an
> > unclean shutdown. ( all the other explained it quite well )
> >
> > The most promising FS is Reiserfs v4
> > http://www.namesys.com/v4/v4.html
> >
> > If you cant wait I suggest XFS or JFS.
>
> ReiserFS may seem "promising," but I wouldn't touch it for DBMS work
> for quite some time to come.
>
> Its design has always been directed to the efficient handling of tiny
> files, and I don't see version 4 changing that.  That's not ideal for
> PostgreSQL, because it tends to access fairly large files.

I wouldn't be so quick to judge. While you are correct that ReiserFS v3
had small files in mind during its design process, v4 is attempting to
be the best of both worlds. This is evident by its "extents" mode, which
if I recall correctly is one method that XFS uses to get decent
performance with large files. (Take a look at:
http://kerneltrap.org/node/view/741)

>
> ReiserFS has a history of losing data when crashes take place (e.g. -
> unclean shutdown).  I haven't experienced any _enormous_ horrors, but
> have experienced enough small problems that I'm not interested in
> having DBMS files on it...

ReiserFS v3 by default only journals meta-data, so this may be what your
referring to, which is the same problem you would get with EXT3 in
write-back mode.

However Reiser4 is a completely different beast, in that its fully
atomic, so AFAIK it has no concept of meta-data journaling, data
journaling, or any of that. Writes either complete successfully or they
don't, so in theory Reiser4 should be the "safest" file system available
for Linux in this regard. According to http://fsbench.netnation.com,
Reiser4 is already showing _very_ impressive performance. Though it uses
more CPU than most of the other file systems, its so much faster that it
almost evens out. Having said all this, Reiser4 is no where near
production ready, but it will be something to keep an eye on.

If your database is I/O bound, XFS would be a good choice, if its CPU
bound, JFS (JFS tends to use the least amount of CPU, at the expense of
some speed).

I would be very interested in seeing actual PGBENCH results with
databases on the different file systems, thats the only way you will
know for sure which file system is best for the task.

--
Best Regards,

Mike Benoit
NetNation Communications Inc.
Systems Engineer
Tel: 604-684-6892 or 888-983-6600
 ---------------------------------------

 Disclaimer: Opinions expressed here are my own and not
 necessarily those of my employer