RE: Important: Oracle processes taking lots of CPU

  • From: "Cary Millsap" <cary.millsap@xxxxxxxxxx>
  • To: <ORACLE-L@xxxxxxxxxxxxx>
  • Date: Wed, 24 Nov 2004 13:21:58 -0600

Both the time spent in user mode (%usr) spinning for a latch and the =
spent in kernel mode (%sys) contribute to the c statistic shown in =
SQL trace files.

If your system is enduring a lot of preemptions (context switching), you =
also detect that in your extended SQL trace data by noticing that a
significant proportion of your total response time is unaccounted for. =
can detect unaccounted-for time in your extended SQL trace data, but I =
think there's any way to detect it Oracle's V$/X$ data.

Cary Millsap
Hotsos Enterprises, Ltd.
* Nullius in verba *

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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx =
On Behalf Of John Kanagaraj
Sent: Wednesday, November 24, 2004 1:13 PM
To: 'New DBA'; ORACLE-L@xxxxxxxxxxxxx
Subject: RE: Important: Oracle processes taking lots of CPU

Hi New DBA,

>As I understand, the CPU is used while performing
>LIOs, doing calculation, sorts or while spinning for
>the latches. My understanding might be wrong! Since
>there aren't enough LIOs or complex calculations
>involved I thought that spinning for latches might be
>causing excessive CPU.=20

Spinning does cause CPU issues. I believe that if you have many =
and comparatively lesser number of processors, then you might have a lot =
CPU consumption that is unaccounted for as cycles used for process =
switching is not accounted in oracle. You will have to then look at 'sar =
( look for high %sys), 'sar -q' (look for high run queue size and =
and 'sar -w' (look for excessive process switches).

Let us know if this helps,
John Kanagaraj <><
DB Soft Inc
Phone: 408-970-7002 (W)   - Manuals for DBAs (English only) - Manual for Life (in English, Deutsch, =
Italian, Spanish, Portugese, Turkish,...)

** The opinions and facts contained in this message are entirely mine =
and do
not reflect those of my employer or customers **


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