Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com> writes:
> I'm wildly guessing that, the # of pages itself seems to be
> a bigger factor than the sequential/random nature.
No, they're both important: fetching N pages in sequence is way cheaper
than fetching the same number of pages scattered all over. This is
partly because you reduce seeking at the hardware level, and partly
because sequential reads cue the kernel to do read-ahead, allowing
overlap of I/O and computation.
regards, tom lane