pwing@student.umass.edu writes:
> I am running three ways: sequential scan, bitmap index scan and index scan.
> The I/O cost for the index scan is 24+ times more than the other two. I do not
> understand why this happens. If I am using a clustered index, it is my
> understanding that there should be no need to retrieve a single page multiple
> times, as tuples are sorted. Am I misunderstanding something?
How long ago did you cluster the table? It sounds like it has degraded
far away from a fully-ordered state.
regards, tom lane