Re: another autovacuum scheduling thread

Still catching up on the latest discussion, but here's a v8 patch that
amends the DEBUG3 in relation_needs_vacanalyze() to also log the score. I
might attempt to add some sort of brief documentation about autovacuum
prioritization next.

From skimming the latest discussion, I gather we might want to consider
re-sorting the list periodically. Is the idea that we'll re-sort the
remaining tables in the list, or that we'll basically restart
do_autovacuum()? If it's the latter, then we'll need to come up with some
way to decide when to stop for the current database. Right now, we just go
through pg_class and call it a day.

--
nathan