Re: CPU COSTING
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 23 Apr 2004 15:07:34 +0100
"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
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: "Khedr, Waleed" <Waleed.Khedr@xxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
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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