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/
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