Message-ID: <46528A37.6040309@cybertec.at>
Date: Tue, 22 May 2007 08:14:15 +0200
From: Zoltan Boszormenyi <zb@cybertec.at>
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To: "Jim C. Nasby" <decibel@decibel.org>
CC: PFC <lists@peufeu.com>, pgsql-performance@postgresql.org
Subject: Re: Postgres Benchmark Results
References: <op.tsmrv71ecigqcu@apollo13> <46508CB9.1040404@cybertec.at>
	<20070521210125.GM62346@nasby.net>
In-Reply-To: <20070521210125.GM62346@nasby.net>
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Jim C. Nasby írta:
> 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.
>   

It could well be the case.

> Each transaction committed essentially requires one revolution of the
> drive with pg_xlog on it, so a 15kRPM drive limits you to 250TPS.
>   

By "revolution", you mean one 360 degrees turnaround of the platter, yes?
On the other hand, if you have multiple clients, isn't the 250 COMMITs/sec
limit is true only per client? Of course assuming that the disk subsystem
has more TCQ/NCQ threads than the actual number of DB clients.

> 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.
>   

I haven't touched the FS options.
I can even use ext2 if I want non-recoverability. :-)

-- 
----------------------------------
Zoltán Böszörményi
Cybertec Geschwinde & Schönig GmbH
http://www.postgresql.at/