Re: When to use bitmap indexes

"Michiel Brunt" <mbrunt_at_inergy.nl> wrote in message news:<9oet4l$252u$1_at_scavenger.euro.net>...
> 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.

My opinion is that product_key is perfect example for bitmap index. However with customers I'm not sure. You can try, but I would prefer not using bitmap index for this column.

--
_________________________________________

Dusan Bolek, Ing.
Oracle team leader

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