Re: CPU Wait troubleshoot

From: Franck Pachot <franck@xxxxxxxxxx>
To: backseatdba@xxxxxxxxx, mark.powell2@xxxxxxx
Date: Wed, 13 Apr 2016 05:47:02 +0000

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@xxxxxxxxx> 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@xxxxxxx>
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@xxxxxxxxxxxxx [mailto:
oracle-l-bounce@xxxxxxxxxxxxx] *On Behalf Of *Martin Berger
*Sent:* Tuesday, April 12, 2016 1:41 PM
*To:* backseatdba@xxxxxxxxx
*Cc:* oracle-l@xxxxxxxxxxxxx
*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@xxxxxxxxx>:

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@xxxxxxxxx
                                +43 660 660 83306 <+4366066083306>
@martinberx <https://twitter.com/martinberx>
http://berxblog.blogspot.com

References:
- CPU Wait troubleshoot
  - From: Jeff Chirco
- Re: CPU Wait troubleshoot
  - From: Martin Berger
- RE: CPU Wait troubleshoot
  - From: Powell, Mark
- Re: CPU Wait troubleshoot
  - From: Jeff Chirco

Re: CPU Wait troubleshoot

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