On 02/07/10 13:31, Bruce Momjian wrote:
Leonardo F wrote:
I'm trying to find more docs that explain the "improvements" of
bitmap indexes in other products... but most of what I've found
talks about bitmapAND/OR.... which is something that is very
cool, but that postgres already does even with btree indexes...
or index creation time/size, which are, for the moment, the only
things that I'm pretty confident the patch would actually provide.
I think a real limitation of on-disk bitmap indexes is that they are
only feable for low cardinality columns, while btree handles all column
types.
I recall that for (some/most? of) those low cardinality cases, (on disk)
bitmap indexes would perform better too. I think the size saving alone
is a huge win for serious data warehousing situations. On the other hand
problems I recall are possibly reduced UPDATE/DELETE performance and
issues with CREATE INDEX CONCURRENTLY and also complications with VACUUM
(altho these last two may have been sorted - I've lost touch with what
was in the most recent patches).
regards
Mark
