Re: [Testperf-general] dbt2 & opteron performance

On Fri, Jul 29, 2005 at 01:11:35PM -0700, Mark Wong wrote:
> On Fri, 29 Jul 2005 14:57:42 -0500
> "Jim C. Nasby" <decibel(at)decibel(dot)org> wrote:
>
> > On Fri, Jul 29, 2005 at 12:51:57PM -0700, Mark Wong wrote:
> > > > Not sure I fully understand what you're trying to say, but it seems like
> > > > it might still be worth trying my original idea of just turning all 80
> > > > disks into one giant RAID0/striped array and see how much more bandwidth
> > > > you get out of that. At a minimum it would allow you to utilize the
> > > > remaining spindles, which appear to be unused right now.
> > >
> > > I have done that before actually, when the tablespace patch came out. I
> > > was able to get almost 40% more throughput with half the drives than
> > > striping all the disks together.
> >
> > Wow, that's a pretty stunning difference... any idea why?
> >
> > I think it might be very useful to see some raw disk IO benchmarks...
>
> A lot of it has to do with how the disk is being accessed. The log is
> ideally doing sequential writes, some tables only read, some
> read/writer. The varying access patterns between tables/log/indexes can
> negatively conflict with each other.

Well, seperating logs from everything else does make a lot of sense.
Still interesting that you've been able to see so much gain.

> Some of it has to do with how the OS deals with file systems. I think
> on linux is there a page buffer flush daemon per file system. A real OS
> person can answer this part better than me.

So, about testing with FreeBSD.... :P
--
Jim C. Nasby, Database Consultant decibel(at)decibel(dot)org
Give your computer some brain candy! www.distributed.net Team #1828

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