Re: CPU Wait troubleshoot

From: Franck Pachot <franck_at_pachot.net>
Date: Wed, 13 Apr 2016 05:47:02 +0000
Message-ID: <CAK6ito29G_dn+yFtiJHgT+ahtB+cKTsETw1q6uDwR9Cz0i630Q_at_mail.gmail.com>

Hi,
As 'Wait for CPU' Is calculated from difference between DB time and all wait events, it may also include some system calls that are not instrumented with wait events. It's rare but still happens. If it's not in ASH then it's not OS run queue. Probably some idle event not instrumented.
Regards,
Franck
Le mer. 13 avr. 2016 à 02:09, Jeff Chirco <backseatdba_at_gmail.com> a écrit :

> No parallelism on this. And ASH does not show this number active
> sessions, it only shows 4.
>
> On Tue, Apr 12, 2016 at 12:17 PM, Powell, Mark <mark.powell2_at_hpe.com>
> wrote:
>
>> Is PQO in use on your system? The submission of a query which
>> gets/demands a very high degree of parallelism can cause a spike in CPU
>> while the query slaves are launched and running.
>>
>>
>>
>> What does the ASH report show for this time period? If the information
>> is anywhere I would think this is the place to look.
>>
>>
>>
>>
>>
>> *From:* oracle-l-bounce_at_freelists.org [mailto:
>> oracle-l-bounce_at_freelists.org] *On Behalf Of *Martin Berger
>> *Sent:* Tuesday, April 12, 2016 1:41 PM
>> *To:* backseatdba_at_gmail.com
>> *Cc:* oracle-l_at_freelists.org
>> *Subject:* Re: CPU Wait troubleshoot
>>
>>
>>
>> Jeff,
>> Spikes in graphs which show averages are ... dangerous.
>> But nevertheless you should be able to identify "something" those
>> sessions have in common.
>> My first checks are sql_id, or program/action/module/... (your
>> application is properly instrumented?)
>> or in general anything you can use to identify why these sessions are
>> special, especially in comparison to the "ordinary" 2-5 active sessions.
>>
>> If you find anything special in those sessions, we all together can drill
>> down to explain what's going on in your system.
>>
>> Martin
>>
>>
>>
>> 2016-04-12 19:16 GMT+02:00 Jeff Chirco <backseatdba_at_gmail.com>:
>>
>> Looking for some help on how to troubleshoot this spike in CPU Wait.
>> Every so often it will see this large spike and I am not sure how to find
>> out what it is related to or why it is happening. It spike up to 400 active
>> sessions when normally we only around 2 - 5. When I click on the graph to
>> drill in it only show the CPU usage and nothing near 400 active sessions.
>> What else do I need to look out to figure this out. Thanks in advanced.
>>
>>
>> [image: Inline image 1]
>>
>> Jeff
>>
>>
>>
>>
>>
>> --
>>
>> Martin Berger martin.a.berger_at_gmail.com
>> +43 660 660 83306 <+4366066083306>
>> _at_martinberx <https://twitter.com/martinberx>
>> http://berxblog.blogspot.com
>>
>
>

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Received on Wed Apr 13 2016 - 07:47:02 CEST