In a pure star schema case, you put a bitmap index on
all foreign keys of the fact table.
I've done a lot of test on 8.0.5 and the optimiser was
using star_transformation.
The more dimensions involved in the query the faster
it executed.
Sometimes with only 2 dimensions, the optimiser was
not using star_transformation.
I had no problem with the bitmap indexes on the
foreign keys.
- Joe Frohne <joe_at_rawsonoaks.com> a écrit : > Hi
Listers,
>
> I have a quick question about setting up a star
> schema datawarehouse using
> star_transformation_enabled. I have a fact table
> and several dimension
> tables. My fact table is a personal table and some
> of the dimension
> tables are grades and test scores. The fact table
> has the students id and
> it is linked to all of the dimension tables with the
> id field. To use the
> star transformation I need to have a bitmapped index
> on the id field in
> the personal table. This is going to be a totaly
> unique field.
>
> The question is, what is the downside of a bitmapped
> index on such a
> field? Is my thought process correct that there
> needs to be a bitmaped
> index on this field to utilize the star
> transformation?
>
> Thank You for any insight!
>
> Joe
>
> --
>
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
> Joe Frohne
> joe_at_rawsonoaks.com
> OCP Database Administrator
> www.rawsonoaks.com
>
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
>
> --
> Author: Joe Frohne
> INET: joe_at_rawsonoaks.com
>
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Stephane Paquette
DBA Oracle
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spaquette_at_houra.fr
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Received on Mon Jul 24 2000 - 09:03:09 CDT
