Re: [PERFORM] Quad processor options

On Tue, 11 May 2004, Bjoern Metzdorf wrote:

> Hi,
>
> I am curious if there are any real life production quad processor setups
> running postgresql out there. Since postgresql lacks a proper
> replication/cluster solution, we have to buy a bigger machine.
>
> Right now we are running on a dual 2.4 Xeon, 3 GB Ram and U160 SCSI
> hardware-raid 10.
>
> Has anyone experiences with quad Xeon or quad Opteron setups? I am
> looking at the appropriate boards from Tyan, which would be the only
> option for us to buy such a beast. The 30k+ setups from Dell etc. don't
> fit our budget.
>
> I am thinking of the following:
>
> Quad processor (xeon or opteron)
> 5 x SCSI 15K RPM for Raid 10 + spare drive
> 2 x IDE for system
> ICP-Vortex battery backed U320 Hardware Raid
> 4-8 GB Ram

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.

But, do you really need more CPU horsepower?

Are you I/O or CPU or memory or memory bandwidth bound? If you're sitting
at 99% idle, and iostat says your drives are only running at some small
percentage of what you know they could, you might be memory or memory
bandwidth limited. Adding two more CPUs will not help with that
situation.

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.

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...

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.