Re: Account DB CPU vs OS CPU

From: Tanel Poder <tanel_at_poderc.com>
Date: Fri, 25 Sep 2009 11:49:02 +0800
Message-ID: <4602f23c0909242049ia22e5f8w4631a9f7f0dbad65_at_mail.gmail.com>

Oracle server processes ask how much CPU they have used (using times() syscall) from OS. Times reports all CPU usage of the process, both user and kernel mode. So no time should be lost there. Of course there may be bugs where some process doesn't ask OS for its CPU usage on time or doesn't add this to system wide stats views.

But if Oracle says A but OS says B about CPU usage - it's always the OS to trust!

Tanel.

On Thu, Sep 24, 2009 at 1:07 PM, LS Cheng <exriscer_at_gmail.com> wrote:

> By the way I understand that when doing I/O CPU is not accounted by Oracle,
> so it might be a the cause of such observation?
>
>
> Thanks
>
> --
> LSC
>
>
>
> On Thu, Sep 24, 2009 at 6:55 AM, LS Cheng <exriscer_at_gmail.com> wrote:
>
>> Hi
>>
>> I have a 4 nodes RAC running on Solaris 10 each with 5 quadcore CPU (or
>> Dual with Threading not sure). Shows 20 CPU in psrinfo.
>>
>> A few days ago we were running with two nodes only and one node during
>> peak time was consuming an average of 95% CPU. There are 15 instances per
>> node so I obtained DB CPU from time model for each instance during the peak
>> time (one hour), added them up and got around 45000 seconds. Considering 20
>> CPU there should be around 72000 seconds CPU so from Oracle point of view
>> 62.5% of CPU was being used in average but from OS point of view 95%.
>>
>> There arent any more application running except Patrol agent and Grid
>> agent, so how trustie is DB CPU statistic?
>>
>>
>> Thanks!
>>
>> --
>> LSC
>>
>>
>

-- 
Tanel Poder
http://blog.tanelpoder.com

--
http://www.freelists.org/webpage/oracle-l

Received on Thu Sep 24 2009 - 22:49:02 CDT