Re: Bitmap indexes - when to use?

The low cardinality reference is a relative term. I think that if the ratio of distinct values to total row is below 1% (50/6000000 < 1%), then this is a candidate for a binary index. The volatility of the column is also important, a change in the column will have interesting results in the bitmap index. (The lower the cardinality, the faster the bitmap index will grow with updates). Performance can be amazing (quick). A regular B-tree index does not work well with low cardinality, bitmap indexes handle this better.

HTH
    James

In article <37443072.EA1CF508_at_mci.com>,   MKB <mohammed.bhatti_at_mci.com> wrote:
> I'd like to know if using bitmap indexes on a column such as STATE
would
> be a good idea. My impression is that bitmaps would be useful only in
> situations with low cardinality in the column (yes/no, on/off etc).
> With a STATE column in a table of, say, 6 million rows, you could
have,
> at most, 50 distinct values. Would it be better in this case just to
go
> with a regular B-tree index? BTW, in this case the STATE column in
the
> main table is an FK to the STATE_CD lookup table and this is for a DSS
> type db using partitions.
>
> (Oracle 8.0.5 on Solaris)
>
> Any input appreciated.
>
> Thanks
>
> mkb
>
>

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