RE: Density calculation. Was: Incorrect cardinality estimate

Ok then, Oracle is adjusting density by deviation.

The question is how Oracle decides unpopular values. Calculations show that the decision is discrete: The value is either in or out, there appears to be no weighting factor.  

-----Original Message-----

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of jonathan_at_jlcomp.demon.co.uk Sent: 25. janúar 2007 10:59
To: oracle-l_at_freelists.org
Subject: Re: Density calculation. Was: Incorrect cardinality estimate

See Cost Based Oracle Fundamentals p.172

In purely descriptive terms, the density is:

    sum of the square of the frequency of the non-popular values /     (number of non-null rows * number of non-popular non-null rows)

It is interesting to note that in the case of the original poster, eliminating the popular values made the density go UP, when you would expect it to go down.

Regards
Jonathan Lewis
Fyrirvari/Disclaimer
http://www.landsbanki.is/disclaimer
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http://www.freelists.org/webpage/oracle-l Received on Thu Jan 25 2007 - 06:34:07 CST