In article <968n4c$tqh$1_at_nnrp1.deja.com>,
dmnwork_at_my-deja.com wrote:
>
>
> Should a STATE column be indexed using a bitmap index or b-tree index?
> Is 50 too high a cardinality to consider using a bitmap index? Any
rule
> of thumb here, or should I create both types of index and "set timing
> on" to test the speed of queries using that index?
>
> Clearly, a GENDER column with only two unique values would be an
> unambiguous candidate for a bitmap index; past what number does the
> utility of a bitmap index provide diminishing returns?
>
> Thanks very much.
>
> - Dana
>
I think the answer depends on how many different state values will
likely exist in the table? And how much update activity exists on the
table? Since a bit map entry covers multiple rows the presence of
bitmap indexes on an updated table can adversely affect update
performance. Also bitmap indexes are most useful when they can be
combined with another bitmap index so if the queries that reference the
state column only reference the state column or the state and unindexed
columns then they is no reason to use a bitmap over a b-trieve index.
--
Mark D. Powell -- The only advice that counts is the advice that
you follow so follow your own advice --
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Received on Mon Feb 12 2001 - 08:18:05 CST
