Re: Oracle CPU_COUNT

Carol wrote:

> I have a Compaq DL580 server with 2 Xeon P1.7 processors; the server
> is set up with hyper threading. I have installed Win2K Advanced
> Server and Oracle 9.0.2 running a live database. When I open task
> manager it appears that I have 4 processors and they are all getting
> used. I checked oracles CPU_COUNT and it is set at 4.

Hyperthtreading basics explained at:
http://www.intel.com/technology/hyperthread/

Because this is enabled, it is likely the cause why the Oracle CPU_COUNT is set to 4..  

> Will I see a performance improvement if I turn off the hyper threading
> and change the CPU_COUNT to 2?

Unknown. I think that this can only be answered if you try it.

Part of the answer to this question is not as much changing the Oracle CPU_COUNT, but whether or not Oracle's machine code on an Intel CPU are "hyperthread friendly".

Part of the answer is how the NT kernel implements hyperthreading.

Even if you do get answers to these, I believe that the final proof is still in microwaving the pudding and see whether it explodes or not.

> I have read that it is not recommended to change the CPU_COUNT

Correct.

> would I
> be better uninstalling and re-installing oracle and let it pick this
> up for itself or is there another option, I can afford to have the
> database down for a weekend?

What are you trying to fix? If there is a performanc issue with the Oracle database, then you should rather atteppt to identify the cause of that first, before wanting to change low level hardware configuration.. and in the process introducing additional variables into the performance equation.

Oracle is likely thinking there are 4 CPU's as that is what the NT kernel is telling it. What does NT's performance manager says about CPU's?

If you really want, disable hyperthreading in the NT configuration, reboot and see what Oracle thinks about it and how it responds performance wise. But I would still rather first identify the actual performance problem first, before messing at that level with the platform.

If it ain't broke, don't fix it.

or..

If you're not sure it ain't broke, don't try to fix it with a Large Hammer. :-)

--
Billy