Re: bitmap indexes - performance

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