Re: Index key compression - performance benefits?

I agree with David's comments on considering bitmap indices even if the cardinality is not very low, but bitmap indexes can be disastrous for performance if there are *any* INSERT, UPDATE, or DELETE operations expected against the table in question. While bitmap indexes support insertions, updates, and deletions transparently, they don't do it with any sense of urgency, so to speak. So, comparison testing should include samples of modifications as well, to be sure that this is proven empirically.

And, if you are not on 10g or above, modifications to bitmap indexes typically cause them to become less compact and less efficient over time, necessitating periodic rebuilds. If you're on 10g or above, Oracle took care of this...

David Aldridge wrote:
> In the context of memory requirements and disk bandwidth the index size
> is rather a critical issue though, so there is a correlation between
> segment size and performance.
>
> Fortunately this issue is very amenable to performance testing of the
> two alternatives. You might also consider bitmap indexes, even for
> columns with a relatively high number of distinct values. Throw those
> into the mix and you have the basis for a very nice little comparison.
>
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