Re: Poor performance of btrfs with Postgresql

> -----Original Message-----
> From: pgsql-general-owner(at)postgresql(dot)org [mailto:pgsql-general-
> owner(at)postgresql(dot)org] On Behalf Of Toby Corkindale
> Sent: Thursday, April 21, 2011 12:22 AM
> To: luv-main; pgsql-general(at)postgresql(dot)org
> Subject: [GENERAL] Poor performance of btrfs with Postgresql
>
> I've done some testing of PostgreSQL on different filesystems, and with
> different filesystem mount options.
>

{snip}

>
> I'm curious to know if anyone can spot anything wrong with my testing?

{snip}

> (Tested on Ubuntu Server - Maverick - Kernel 2.6.35-28)

Don't take this the wrong way - I applaud you asking for feedback. BTW ->
Have you seen Greg Smiths PG 9.0 high performance book ? it's got some
chapters dedicated to benchmarking.

Do you have battery backed write cache and a 'real' hardware raid card?
Not sure why your testing with raid 0, but that is just me.

You also did not provide enough other details for it to be of interest to
many other people as a good data point. If you left all else at the defaults
then might just mention that.

Did you play with readahead ?

XFS mount options I have used a time or two... for some of our gear at work:

rw,noatime,nodiratime,logbufs=8,inode64,allocsize=16m

How was the raid configured ? did you do stripe/block alignment ? might not
make a noticeable difference but if one is serious maybe it is a good habit
to get into. I haven't done as much tuning work as I should with xfs but a
primer can be found at :
http://oss.sgi.com/projects/xfs/training/xfs_slides_04_mkfs.pdf

Getting benches with pg 9 would also be interested because of the changes to
pgbench between 8.4 and 9.0, although at only about 230 tps I don't know how
much a difference you will see, since the changes only really show up when
you can sustain at a much higher tps rate.

Knowing the PG config, would also be interesting, but with so few disks and
OS, xlogs, and data all being on the same disks .... well yeah it's not a
superdome, but still would be worth noting on your blog for posterity sake.

Right now I wish I had a lot of time to dig into different XFS setups on
some of our production matching gear - but other projects have me too busy
and I am having trouble getting our QA people loan me gear for it.

Heck I haven't tested ext4 at all to speak of - so shame on me for that.

To loosely quote someone else I saw posting to a different thread a while
back "I would walk through fire for a 10% performance gain". IMO through
proper testing and benchmarking you can make sure you are not giving up 10%
(or more) performance where you don't have to - no matter what hardware you
are running.

-Mark

>
> Cheers,
> Toby
>
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