Re: CPU Costing

Anurag Varma wrote:

>"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
>
>
>

Thanks. I'll try system_stats tomorrow.

Someone doing documentation at Oracle owes you a lunch.

-- 
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)