RE: question about cpu usage (fwd)

dont see any harm in putting this on oracle-l. cary probably just didnt do a reply to all. the chart is very useful.

• Forwarded Message: -------------- From: "Cary Millsap" <cary.millsap_at_hotsos.com> To: <ryan_gaffuri_at_comcast.net> Subject: RE: question about cpu usage Date: Fri, 22 Oct 2004 20:06:54 +0000

Ryan,

Good question actually. It depends on how many CPUs are in there. If you have a copy of "Optimizing Oracle Performance" handy, check out table 9-3 on page 260. What it says is that you can expect performance to vary unpredictably on a 1-CPU machine when CPU utilization exceeds 50%. On a 2-CPU machine, the magic number is about 57.7%. On a 4-CPU machine, it's 66.5%. The table lists "knee in the curve" numbers for CPU counts ranging from 1 to 128.

The whole section called "Behavior of M/M/m Systems" (pp254-266) should be of interest to you.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
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-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of ryan_gaffuri_at_comcast.net
Sent: Friday, October 22, 2004 2:56 PM
To: oracle-l_at_freelists.org
Subject: question about cpu usage

I'm not a hardware guy or sys admin person so forgive me if this is a stupid question. Leaving out all other variables(such as IO), should I expect performance to be the same in a databse if the server it is riding at is at 90% cpu usages as opposed to 10%? since there would still be spare cycles? Or is there a declining returns as you get closing to the maximum available cpu usage?

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