> http://en.wikipedia.org/wiki/Cluster_sampling
> http://en.wikipedia.org/wiki/Multistage_sampling
>
> I suspect the hard part will be characterising the nature of the
> non-uniformity in the sample generated by taking a whole block. Some
> of it may come from how the rows were loaded (e.g. older rows were
> loaded by pg_restore but newer rows were inserted retail) or from the
> way Postgres works (e.g. hotter rows are on blocks with fewer rows in
> them and colder rows are more densely packed).
I would have thought that as VACUUM reclaims space it levels that issue in
the long run and on average, so that it could be simply ignored?
> I've felt for a long time that Postgres would make an excellent test
> bed for some aspiring statistics research group.
I would say "applied statistics" rather than "research". Nevertheless I
can ask my research statistician colleagues next door about their opinion
on this sampling question.
--
Fabien.