Re: CPU Time calculation in AWR Reports

In this case it should be the same at the end of the day. Shouldn't it be?

After Jonathan posted his AWR observations, I couldn't reproduce similar
behavior and don't believe the time is calculated as *CPU used by this
session + recursive calls cpu usage*. At least not always. Here is a
post Recursive
Calls <http://vsadilovskiy.wordpress.com/2007/11/05/recursive-calls/> that
demonstrates differences in reporting recursive calls CPU usage in various
tools.

I agree that the source of *CPU used by this session* value in v$sysstat
that is *definitely used* to report *CPU time* by Statspack might
be different from the source of the *DB CPU* from v$sys_time_model that *I
think* is used by AWR to report the same. The lack of definitive information
about different DB usage patterns, doesn't allow clear demonstration of
their correlation.

Vlad Sadilovskiy
Oracle Database Tools
Web site: http://www.fourthelephant.com
Blog: http://vsadilovskiy.wordpress.com


On 11/2/07, LS Cheng <exriscer@xxxxxxxxx> wrote:
>
> I think the difference may be because v$sysstat is refreshed after a call
> is completed but in SYS_TIME_MODEL_CPU it gets refreshed every 3 seconds
>
>
> Thanks
>
> --
> LSC
>
> On Nov 1, 2007 6:10 PM, Tanel Poder < tanel.poder.003@xxxxxxx> wrote:
>
> > Well you can trace the awrrpt run...
> >
> > I suspect (but don't know for sure) that AWR uses
> > DBA_HIST_SYS_TIME_MODEL
> > for its CPU info... V$SYS_TIME_MODEL CPU values can differ from
> > V$SYSSTAT
> > ones...
> >
> > SQL> select
> >  2     a.value/1000000 time_model_seconds,
> >  3     b.value/10000   sysstat_seconds,
> >  4     a.value/1000000 - b.value/10000 missing_seconds
> >  5  from
> >  6     v$sys_time_model a,
> >  7     v$sysstat b
> >  8  where
> >  9     a.stat_name = 'DB CPU'
> >  10  and b.name = 'CPU used by this session'
> >  11  /
> >
> > TIME_MODEL_SECONDS SYSSTAT_SECONDS MISSING_SECONDS
> > ------------------ --------------- ---------------
> >        126.997282          4.6276      122.369682
> >
> >
> > --
> > Regards,
> > Tanel Poder
> > http://blog.tanelpoder.com
> >
> >
> > > -----Original Message-----
> > > From: oracle-l-bounce@xxxxxxxxxxxxx
> > > [mailto:oracle-l-bounce@xxxxxxxxxxxxx ] On Behalf Of Luis
> > > Fernando Cerri
> > > Sent: Thursday, November 01, 2007 23:20
> > > To: oracle-l@xxxxxxxxxxxxx
> > > Subject: CPU Time calculation in AWR Reports
> > >
> > > Hello, list.
> > >
> > > At Statspack age, 'CPU Time' value in section 'Top 5 Timed
> > > Events' was calculated as the difference of 'CPU used by this
> > > session' values between two snapshots:
> > >
> > >                        select 'CPU' , (e.value-b.value)/100 time
> > >                          from stats$sysstat b, stats$sysstat e
> > >                         where e.snap_id         = :v_eid
> > >                           and b.snap_id         = :v_bid
> > >                           and e.name            = 'CPU used
> > > by this session'
> > >                           and b.name            = 'CPU used
> > > by this session';
> > >
> > >
> >
> >
> >  --
> > http://www.freelists.org/webpage/oracle-l
> >
> >
> >
> >
>
>

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