Re: Quad processor options - Mailing list pgsql-performance

On Tue, 11 May 2004, Bjoern Metzdorf wrote:

> scott.marlowe wrote:
>
> > Well, from what I've read elsewhere on the internet, it would seem the
> > Opterons scale better to 4 CPUs than the basic Xeons do.  Of course, the
> > exception to this is SGI's altix, which uses their own chipset and runs
> > the itanium with very good memory bandwidth.
>
> This is basically what I read too. But I cannot spent money on a quad
> opteron just for testing purposes :)

Wouldn't it be nice to just have a lab full of these things?

> > If your I/O is saturated, then the answer may well be a better RAID
> > array, with many more drives plugged into it.  Do you have any spare
> > drives you can toss on the machine to see if that helps?  Sometimes going
> > from 4 drives in a RAID 1+0 to 6 or 8 or more can give a big boost in
> > performance.
>
> Next drives I'll buy will certainly be 15k scsi drives.

Better to buy more 10k drives than fewer 15k drives.  Other than slightly
faster select times, the 15ks aren't really any faster.

> > In short, don't expect 4 CPUs to solve the problem if the problem isn't
> > really the CPUs being maxed out.
> >
> > Also, what type of load are you running?  Mostly read, mostly written, few
> > connections handling lots of data, lots of connections each handling a
> > little data, lots of transactions, etc...
>
> In peak times we can get up to 700-800 connections at the same time.
> There are quite some updates involved, without having exact numbers I'll
> think that we have about 70% selects and 30% updates/inserts.

Wow, a lot of writes then.

> > If you are doing lots of writing, make SURE you have a controller that
> > supports battery backed cache and is configured to write-back, not
> > write-through.
>
> Could you recommend a certain controller type? The only battery backed
> one that I found on the net is the newest model from icp-vortex.com.

Sure, adaptec makes one, so does lsi megaraid.  Dell resells both of
these, the PERC3DI and the PERC3DC are adaptec, then lsi in that order, I
believe.  We run the lsi megaraid with 64 megs battery backed cache.

Intel also makes one, but I've heard nothing about it.

If you get the LSI megaraid, make sure you're running the latest megaraid
2 driver, not the older, slower 1.18 series.  If you are running linux,
look for the dkms packaged version.  dkms, (Dynamic Kernel Module System)
automagically compiles and installs source rpms for drivers when you
install them, and configures the machine to use them to boot up.  Most
drivers seem to be slowly headed that way in the linux universe, and I
really like the simplicity and power of dkms.

I haven't directly tested anything but the adaptec and the lsi megaraid.
Here at work we've had massive issues trying to get the adaptec cards
configured and installed on, while the megaraid was a snap.  Installed RH,
installed the dkms rpm, installed the dkms enabled megaraid driver and
rebooted.  Literally, that's all it took.