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Home -> Community -> Mailing Lists -> Oracle-L -> RE: CPU COSTING
So the buffer cache has no impact on the stats.=20
Was wondering how this system stats get calculated, it has to be = collected by the individual sessions themselves and then all the = collected numbers get summarized/correlated into one set of numbers = (system level).
Waleed
-----Original Message-----
From: Jonathan Lewis [mailto:jonathan_at_jlcomp.demon.co.uk]
Sent: Friday, April 23, 2004 10:59 AM
To: oracle-l_at_freelists.org
Subject: Re: CPU COSTING
Not quite -
The new cost model allows Oracle to work out a better balance between the time taken for a single and multi-block read -- which is what people used to use o_i_c_a for.
It does not (yet) allow for the fact that the buffer cache exists. Consequently you need to consider opt_ind_cache still; and review the value for o_i_c_a, view it as an indicator of the percentage of table I/Os that will turn=20 into real physical read requests.
10g has indications that it will also consider the recent history of per-segment cache benefits to modify costs and plans - but I don't think it's enabled in the current release.
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=20 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
So for reads (i/o0 it measures the logical reads that might get =3D
translated to physical or not. It's affected by the buffer cache, and =
=3D
this makes sense.
So as you said, any changes/tuning to oica and oic (opt_ind_cache) might =
=3D
need to be altered again.
Waleed
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