Shridhar Daithankar <shridhar_daithankar@persistent.co.in> writes:
> Would it be possible to have a vacuum variant that would just shuffle thr.
> shared buffers and not touch disk at all?
What would be the use of that? You couldn't predict *anything* about
the coverage. Maybe you find all the free space in a particular table,
but most likely you don't.
In any case an I/O-free vacuum is impossible since once you have decided
to recycle a particular tuple, you don't have any option about removing
the corresponding index entries first. So unless both the table and all
its indexes are in RAM, you will be incurring I/O.
regards, tom lane