Re: how to set optimizer_index_cost_adj and cache parameters?
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 26 Mar 2004 18:21:50 -0000
Waleed
Thanks for the note. You're absolutely right,
I sent in a note to the editor just before
publication because I had missed out the
phrase "of the clustering factor" completely;
unfortunately my explanation of where to
put it wasn't quite clear enough.
I'll send her a correction a.s.a.p
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
----- Original Message -----
From: "Khedr, Waleed" <Waleed.Khedr@xxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Friday, March 26, 2004 5:55 PM
Subject: RE: how to set optimizer_index_cost_adj and cache parameters?
Hi Jonathan,
This is from the article:
"Essentially, this formula tells Oracle the number of block visits (see side
bar) that a process will have to make to collect all the data from the
table. If the selectivity (fraction of the table's data) is X, then it seems
reasonable that the number of index leaf blocks to visit will be X% of the
clustering_factor; and the number of table block visits will also be X%. Add
on the fact that you have to walk from the root to the leaf level just once,
and you have the formula."
I believe it's the other way around:
the number of index leaf blocks = X% of leaf blocks
the number of table block visits = X% of clustering_factor
Regards,
Waleed
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