Re: When to use bitmap indexes

Michiel Brunt wrote:
>
> 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

One of the great things with bitmaps is that they take very little time to create, and very little space - so I'd just bung them on and see how you go...

NB: Bitmaps and changes to the tables do NOT mix at all well

-- 
==============================
Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."