Kris Jurka <books@ejurka.com> writes:
> On Wed, 24 Aug 2005, Tom Lane wrote:
>> This is done (see bitmap index scans).
> Will the optimizer ever choose this plan when dealing with only one index?
Certainly. It's actually likely to prefer a bitmap scan whenever the
query is estimated to fetch more than one percent or so of the table
(although if you are demanding ORDER BY the index order, the crossover
point is higher, since a bitmap scan doesn't deliver sorted output).
Something that probably ought to be on the Open Items list for 8.1
is whether the cost estimation for bitmap vs plain indexscan is OK.
It's entirely likely that we need to do some tweaking to get the
planner to make the right choice.
regards, tom lane
