Date: Mon, 21 May 2007 16:01:25 -0500
From: "Jim C. Nasby" <decibel@decibel.org>
To: Zoltan Boszormenyi <zb@cybertec.at>
Cc: PFC <lists@peufeu.com>, pgsql-performance@postgresql.org
Subject: Re: Postgres Benchmark Results
Message-ID: <20070521210125.GM62346@nasby.net>
References: <op.tsmrv71ecigqcu@apollo13> <46508CB9.1040404@cybertec.at>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <46508CB9.1040404@cybertec.at>
User-Agent: Mutt/1.5.13 (2006-08-11)

On Sun, May 20, 2007 at 08:00:25PM +0200, Zoltan Boszormenyi wrote:
> I also went into benchmarking mode last night for my own
> amusement when I read on the linux-kernel ML that
> NCQ support for nForce5 chips was released.
> I tried current PostgreSQL 8.3devel CVS.
> pgbench over local TCP connection with
> 25 clients and 3000 transacts/client gave me
> around 445 tps before applying NCQ support.
> 680 tps after.
> 
> It went over 840 tps after adding HOT v7 patch,
> still with 25 clients. It topped at 1062 tps with 3-4 clients.
> I used a single Seagate 320GB SATA2 drive
> for the test, which only has less than 40GB free.
> So it's already at the end of the disk giving smaller
> transfer rates then at the beginning. Filesystem is ext3.
> Dual core Athlon64 X2 4200 in 64-bit mode.
> I have never seen such a performance before
> on a desktop machine.

I'd be willing to bet money that the drive is lying about commits/fsync.
Each transaction committed essentially requires one revolution of the
drive with pg_xlog on it, so a 15kRPM drive limits you to 250TPS.

BTW, PostgreSQL sees a big speed boost if you mount ext3 with the option
data=writeback. Note that doing that probably has a negative impact on
data recovery after a crash for non-database files.
-- 
Jim Nasby                                      decibel@decibel.org
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)