RE: CPU COSTING
- From: Wolfson Larry - lwolfs <lawrence.wolfson@xxxxxxxxxx>
- To: "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 22 Apr 2004 18:38:59 -0500
Jonathan, thanks for heads up.
Tanel, by freaked out, I assume you mean performing at warp speed.
Thanks
Larry Wolfson.
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I use cpu costing in 3 of my freaked out test instances ;)
Tanel.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Jonathan Lewis
Sent: Thursday, April 22, 2004 4:06 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: CPU COSTING
I'd forgotten I'd written that note - and
such a long time ago, too.
Does anyone have any idea of how many
people are using cpu_costing ? Could we
take a quick poll ? My impression is that
the number is still pretty low.
In answer to your question: So far I haven't found
any good reasons to not use it - but as it says in
the article, it's almost as scary as switching from
RBO to CBO.
One particular oddity I came across a couple
of weeks ago is that if you are messing about
with multiple block sizes, you may find that the
switch to cpu_costing makes the optimizer to
do more tablescans (or index fast full scans)
on objects in tablespaces with larger block sizes.
Bear in mind that when you migrate to 10g,
you WILL be using cpu_costing unless you
fiddle with a couple of hidden parameters to
disable it.
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk
The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
April 2004 Iceland http://www.index.is/oracleday.php
June 2004 UK - Optimising Oracle Seminar
July 2004 USA West Coast, Optimising Oracle Seminar
August 2004 Charlotte NC, Optimising Oracle Seminar
September 2004 USA East Coast, Optimising Oracle Seminar
September2004 UK - Optimising Oracle Seminar
----- Original Message -----
From: "Wolfson Larry - lwolfs" <lawrence.wolfson@xxxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Thursday, April 22, 2004 4:47 AM
Subject: CPU COSTING
Any reason not to do CPU COSTING as described by Jonathan Lewis?
"You can enable cpu_costing simply by collecting system_statistics for an
appropriate period of time with the dbms_stats package. This records in the
table sys.aux_stats$ values for:
assumed CPU speed in MHz
single block read time in milliseconds
multiblock read time in milliseconds
typical achieved multiblock read."
Full article @ http://www.jlcomp.demon.co.uk/faq/cost_9.html
Thanks
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