Re: HISTOGRAMS , CBO and OLTP

I see Connor has explained how a unique column can have a skewed data distribution. To answer the second paragraph - you don't have to worry about the timing of the histogram/index builds.

However, a though I've just had, it is possible that when Oracle builds the histogram, it MAY be able to use the index to avoid some of the cost of processing if you choose to COMPUTE a histogram for a non-null column. If you find this to be true, let us know.

Regards

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

Coming soon one-day tutorials:
Cost Based Optimisation
Trouble-shooting and Tuning
Indexing Strategies
(see http://www.jlcomp.demon.co.uk/tutorial.html )

____UK_______March 19th
____USA_(FL)_May 2nd

Next Seminar dates:
(see http://www.jlcomp.demon.co.uk/seminar.html )

____USA_(CA, TX)_August

The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html

-----Original Message-----
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Date: 09 February 2003 21:20

>
>Uniqueness indicates that there are less skewed values correct! Under
what circumstances would a skewed column value for a unique column exist.
>
>Another question, what about histograms on indexes itself? If
histograms are generated on columns with skewed values, does it matter when the indexes are generated, before or after? Do indexes on these columns need to be rebuilt.
>
>Thanks
>
>

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Jonathan Lewis
  INET: jonathan_at_jlcomp.demon.co.uk

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).