Gavin Sherry <swm@linuxworld.com.au> writes:
> On Sun, 23 Jul 2006, Tom Lane wrote:
>> However, the main problem I've got with this is that a new index AM is a
>> pretty large burden, and no one's made the slightest effort to sell
>> pghackers on taking this on.
> For low cardinality sets, bitmaps greatly out perform btree.
If the column is sufficiently low cardinality, you might as well just do
a seqscan --- you'll be hitting most of the heap's pages anyway. I'm
still waiting to be convinced that there's a sweet spot wide enough to
justify supporting another index AM. (I'm also wondering whether this
doesn't overlap the use-case for GIN.)
regards, tom lane