When to use bitmap indexes

In our data warehouse we have a large fact table with keys to dimension tables.
Something like:

Product_key      Customer_key     Time_key     Revenue
1                1                1            1000
1                1                2            2000
1                2                2            1000
1                3                1            1000
1                3                2            2000
2                1                1            500
2                1                2            1000
2                2                2            2000

This fact table contains 10 mln records. There are 10.000 products and 500.000 customers The question is wether the use of bitmap indexes is useful.

I heard that the number of distinct values in a column should be less than 10% of the total number of rows in the table. In that case 10.000 / 10.000.000 is fine and even 500.000 / 10.000.000 would work.

Thanks,
Michiel Received on Fri Sep 21 2001 - 03:20:56 CDT