mysql scaling questions

Kris Kennaway kris at FreeBSD.org
Sun Dec 30 05:18:33 PST 2007


Gergely CZUCZY wrote:
> On Sat, Dec 01, 2007 at 12:22:34PM -1000, Jeff Roberson wrote:
>> On Sat, 1 Dec 2007, Gergely CZUCZY wrote:
>>
>>> On Sat, Dec 01, 2007 at 04:06:55PM -0500, Mike Tancsa wrote:
>>>> At 03:56 PM 12/1/2007, Gergely CZUCZY wrote:
>>>>> I don't quite understand the question. It's the very same box, with
>>>>> a dualboot configuration.
>>>> Fire up the 3ware controller's RAID management software and make sure the same write caching strategy is set for FreeBSD and Linux. The
>>>> driver my default to different values.
>>>>
>>>> i.e. under "controller settings" make sure "write cache" and "queuing" are the same values for linux and freebsd.
>>> Let's get back to this on monday. I'm at home now, and the
>>> box is at me workplace, still running a test (i can't reboot it).
>> Also, can you verify with a read-only test to see where it's at?  I have not tested writes with that many threads.  I notice mysql goes much faster 
>> with a fresh table too.  So can you blow away and recreate the sysbench tables and then do read-only?  If that is much slower we'll know there is some 
>> configuration problem or similar.
> It will all be available here:
> http://phoemix.harmless.hu/mysql/

Hi,

Sorry for the late reply, I was on vacation.  I have a couple of 
comments about this:

* You are using some very old mysql versions and trying to compare 
between diferent versions.  New minor releases in the 5.0 series had 
very different performance, and you really need to be using at least 
5.0.45 (I didn't notice a performance change between 5.0.45 and 5.0.51 
but there was a big improvement in every release up to .45.  In 
addition, versions older than (I think) .37 have serious performance bugs).

I appreciate that you might be constrained by local requirements, but 
it's really not meaningful to compare different mysql versions if your 
goal is to study OS performance.

* What database engine are you using?  I have only tested with innodb 
but maybe you are using myisam?  Please provide your exact sysbench 
command lines.

* Compare to my config file here:

http://people.freebsd.org/~kris/scaling/my.cnf

The default mysql config has very poor performance for innodb (you need 
at least innodb_thread_concurrency = 0 to disable some mysql 
brain-death).  Maybe tuning is required for myisam also.

* Also make sure you are using identical config settings on the two systems.

* With the above, please compare read-only mode also (I think Jeff 
already asked you about this but I didnt see a reply).  That will allow 
us to calibrate what is going on.

Kris



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