Jim C. Nasby wrote:
> 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.
>
I thought you were limited to 250 or so COMMITS to disk per second, and
since >1 client can be committed at once, you could do greater than 250
tps, as long as you had >1 client providing input. Or was I wrong?