* pwing@xxxxxxxxxxxxxxxxx (pwing@xxxxxxxxxxxxxxxxx) wrote: > 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? That does seem kind of bad (24+ times is quite a bit). At the same time though, you are having to go through the index when you're doing an index scan whereas you don't with the seq scan, so you're certainly pulling in more data of the disk. I'm a bit mystified why you'd think an index scan to pull half the data from a table is going to be faster than a seq scan anyway though... If you're trying to speed up the query to pull half the records you might want to look into partitioned tables instead, though I doubt it'll get much faster... Thanks, Stephen
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