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RE: CPU COSTING

From: Wolfson Larry - lwolfs <lawrence.wolfson_at_acxiom.com>
Date: Thu, 22 Apr 2004 18:38:59 -0500
Message-ID: <A366E86AF2FBD611AB920002B31E58B0096DC7B5@conmsx07.corp.acxiom.net>


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_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Jonathan Lewis Sent: Thursday, April 22, 2004 4:06 AM
To: oracle-l_at_freelists.org
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

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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Received on Thu Apr 22 2004 - 18:42:24 CDT

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