RE: Bitmap Index
- From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
- To: <oracle.tutorials@xxxxxxxxx>
- Date: Mon, 10 Oct 2005 13:09:02 +0200
Deepak
>In my DWH DB I have a table with few million rows.
>I have a column in the table having 15 distinct
>values. That column is being used in the where
>clause of the queries. What I am interested to know
>is would it be beneficial to create a bitmap index
>on it.
As usually it depends... What does "used" mean? (e.g. equality or inequality)
Do you have other restrictions in your WHERE clause? Which is the distribution
of the 15 values?
As already suggested by Shiva list partitioning (or even other types as
well...) could be a better solution than indexing.
>Is there any specific ratio (distincy values)/(Num of rows)
>at which one must consider creating bitmap indexes rather
>than b-tree indexes?
The choice between bitmap and b-tree indexes is not influenced by something
like "(distincy values)/(Num of rows)". It only depends on the application's
requirements!
HTH
Chris
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