contrib/intarray has an index type which could be what you need.
> I was wondering about index types. Oracle has an index type called a
> 'bitmap' index. They describe this as an index for low cardinality
> fields, where only the cardinal values are indexed in a b-tree, and
> then it uses a bitmap below that to describe rows. They say that this
> type of index is very fast when combined with queries that used the
> indexed row in 'AND' clauses in a sql statement as the index can
> 'mask' the results very fast. I have not been able to benchmark the
> actual effectiveness of this kind of index, but I was wondering if
> anyone has had experience with this an believes it might be a useful
> feature for postgres?
>
> Yes I have a vested interest in this because alot of my searches are
> masked against low cardinality fields 'Y' or 'N' type things where
> this could potentialy benefit me...
>
> Alex Turner
> NetEconomist
>
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