Tom Lane wrote:
>
>I believe that the term "bitmap index" is also used with a different
>meaning wherein it actually does describe a particular kind of on-disk
>index structure, with one bit per table row.
>
>IMHO building in-memory bitmaps (the first idea) is a very good idea to
>pursue for Postgres. I'm not at all sold on on-disk bitmap indexes,
>though ... those I suspect *are* sufficiently replaced by partial
>indexes.
>
>
>
I believe that the benefit of on-disk bitmap indexes is supposed to be
reduced storage size (compared to btree).
In the cases where I have put them to use, they certainly occupy
considerably less disk than a comparable btree index - provided there
are not too many district values in the indexed column.
regards
Mark