"(Even if you have seen an article in Oracle Magazine
that might suggest otherwise)."
Cheeky :-)
- Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
wrote: > The answer to the question you asked is to
> check the dba_indexes view for columns
> distinct_keys and num_rows.
>
> HOWEVER -
>
> It is not sensible to change a b-tree index into
> a bitmap index simply because it has a relatively
> small number of distinct values. (Even if you
> have seen an article in Oracle Magazine that
> might suggest otherwise).
>
> Bitmap indexes tend to degrade catastrophically
> as the underlying table suffers inserts and deletes
> or gets updates to the indexed column. And the
> probability of contention and deadlock on concurrent
> inserts/updates/deletes is very high.
>
> Before going much further down your current path,
> you might like to read a couple of articles I've
> written about bitmap indexes at
> www.dbazine.com
>
>
>
> Regards
>
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>
> Coming soon a new one-day tutorial:
> Cost Based Optimisation
> (see http://www.jlcomp.demon.co.uk/tutorial.html )
>
> Next Seminar dates:
> (see http://www.jlcomp.demon.co.uk/seminar.html )
>
> ____England______January 21/23
>
>
> 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: 20 December 2002 20:16
> the ma
>
>
> >I'm constantly finding, in the database that I'm
> developing/supporting,
> >b-tree indexes on columns with low-cardinality. I
> generally re-create
> said
> >index as a bitmap; however I'd like to go through
> the entire db and
> identify
> >these cases proactively. Is there a way to
> determine the cardinality
> of an
> >index's columns via the dictionary? Also, what
> recommendations do you
> have
> >for determining the cardinality percentage that
> indicates when a
> bitmap
> >should be used? 10%? 20%?
> >
>
>
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.net
> --
> Author: Jonathan Lewis
> INET: jonathan_at_jlcomp.demon.co.uk
>
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Received on Sat Dec 21 2002 - 17:33:37 CST
