"(Even if you have seen an article in Oracle Magazine that might suggest otherwise)."
Cheeky :-) --- Jonathan Lewis <[EMAIL PROTECTED]> 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 > <[EMAIL PROTECTED]> > 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: [EMAIL PROTECTED] > > 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: [EMAIL PROTECTED] (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). > ===== Connor McDonald http://www.oracledba.co.uk http://www.oaktable.net "GIVE a man a fish and he will eat for a day. But TEACH him how to fish, and...he will sit in a boat and drink beer all day" __________________________________________________ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email and Music Charts http://uk.my.yahoo.com -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: =?iso-8859-1?q?Connor=20McDonald?= INET: [EMAIL PROTECTED] 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: [EMAIL PROTECTED] (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).
