Re: When to use bitmap index based on cardinality

From: Christopher M. Day <christopher.day_at_rdbms.freeserve.co.uk>
Date: Sat, 06 Feb 1999 00:13:06 +0000
Message-ID: <36BB8912.F7C4C780@rdbms.freeserve.co.uk>

Cutler,

(A view from 8.0.5.11)
I would agree, up until a couple of days ago ! Check out the proceedings from the OpenWorld'98 conference in SF on www.oracle.com. There was a presentation about using bitmaps on everything but UNIQUE columns.

I tried this on two tables. One contains a unique key for all the households in the UK (hurn key) (b*tree), its child contains the hurn key and a person unique key. I used to have a b*tree on the child hurn column and have since changed it to a bitmap. The result was less storage and an increase in performance...

Chris

cutler_temp_at_usa.net wrote:
>
> I'm on Oracle 7.3.4.2
>
> The Oracle Tuning documentation says this about bitmap indexes:
> <
> Bitmap indexes can substantially improve performance of queries with the
> following characteristics:
>
> The WHERE clause contains multiple predicates on low- or medium-cardinality
> columns....
Received on Fri Feb 05 1999 - 18:13:06 CST