Re: When to use bitmap indexes

Connor,

As one having been contemplating implementing bitmap indexes for a few cases, my curious mind wonders if you would be willing to expound on:

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

Thanks in advance,

Jim Davis

"Connor McDonald" <connor_mcdonald_at_yahoo.com> wrote in message news:3BABBFEA.6E8D_at_yahoo.com...
> 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..."
Received on Sat Sep 22 2001 - 06:56:13 CDT