Re: Help! Bitmap Index

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Mon, 26 Apr 1999 21:32:05 +0100
Message-ID: <925158921.21545.1.nnrp-02.9e984b29@news.demon.co.uk>

Performance benefits from bitmap indexes come from combining several 'bad' indexes in a single query. If your data set is 50% male 50% female, then a query only by gender is bound to be inefficient since it has to access a very large data set.

For some realistic test results on Oracle 7.3 (not yet repeated on 8.0, but coming soon) see the article on my website under the 'features' section.

Jonathan Lewis
Yet another Oracle-related web site: www.jlcomp.demon.co.uk

Alon Peled wrote in message <3724D0EE.58E99438_at_peled.com>...
>
>I have created a bitmap index on the sex column (M/F Values) and
>performance during queries on this column has not been changed.
>The table is 3M in size and tkprof shows that the index is being used.
>Has any one used Bitmap index and got any performance increase?
Received on Mon Apr 26 1999 - 15:32:05 CDT