Re: CPU COSTING

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Fri, 23 Apr 2004 15:07:34 +0100
Message-ID: <019601c4293c$532b9c00$7102a8c0@Primary>

"CPU Costing" specifically estimates the CPU time needed for all operations, so there is a 'CPUCycle count' for a logical I/O, a CPUCycle count for comparing locating a row in a block, a CPUCycle count for skipping over each column in a row to find the right one and so on.

Loosely, when CPUCosting is enabled it's part of enabling the CPU cost model, normally controlled by parameter _optimizer_cost_model, which can be set to IO, CPU, or CHOOSE.

So in fact, the I/O costing changes at the same time, so that (in particular):

cost of t/s = blocks to scan / recorded MBRC *

                        mreadtim / sreadtim + 
                        CPU cost.

I've got a paper coming out on OTN in a couple of weeks that talks about it a bit.

Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

The Co-operative Oracle Users' FAQ
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Original Message ----- From: "Khedr, Waleed" <Waleed.Khedr_at_FMR.COM> To: <oracle-l_at_freelists.org> Sent: Friday, April 23, 2004 2:57 PM Subject: RE: CPU COSTING

Do you know what it (cpu costing) measures : the logical reads or the = physical reads (does the buffer cache affects the numbers)?

Thanks

Waleed

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Received on Fri Apr 23 2004 - 09:06:13 CDT