Re: CPU Costing

"Anurag Varma" <avdbi_at_hotmail.com> wrote in message news:c5d7b.480$WH.354_at_news01.roc.ny...
>
> "Daniel Morgan" <damorgan_at_exxesolutions.com> wrote in message news:1063080455.463722_at_yasure...
> > Setting up a demo for my students for the Fall with the new DBMS_XPLAN
> > built-in package and I am getting the message:
> >
> > "Note: cpu costing is off"
> >
> > Which would be fine if I could figure out how to turn it on or off or
> > set it.
> >
> > A search of tahiti.oracle.com yields only two references to CPU Costing
> > neither of which explains anything related other than a statement that
> > it is user-defined ... user defined ... how?. And a check of
> > v_$parameter indicates that it is not something modifyable in the init.ora.
> >
> > Any help will be appreciated. Thanks.
> >
> > --
> > Daniel Morgan
> > http://www.outreach.washington.edu/ext/certificates/oad/oad_crs.asp
> > http://www.outreach.washington.edu/ext/certificates/aoa/aoa_crs.asp
> > damorgan_at_x.washington.edu
> > (replace 'x' with a 'u' to reply)
> >
>
> Daniel,
>
> imho .. it refers to whether you have gathered the SYSTEM statistics or not.
> Look into the built in package documentation of dbms_stats.gather_system_stats
>
> .. so by default it is off until you gather the stats.
>
> That if run, will gather cpu costing .....
>
> hth
>
> Anurag
>
>

Also: look in http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96533/stats.htm#25643 where it states more clearly (read last two words ;) ... "System statistics enable the optimizer to consider a system's I/O and CPU performance and utilization. For each plan candidate, the optimizer computes estimates for I/O and CPU costs. It is important to know the system characteristics to pick the most efficient plan with optimal proportion between I/O and CPU cost."

Anurag Received on Tue Sep 09 2003 - 00:06:32 CDT