Re: BUG #13750: Autovacuum slows down with large numbers of tables. More workers makes it slower.

Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> David Gould wrote:
>> Anyway, they are not actually vacuuming. They are waiting on the
>> VacuumScheduleLock. And requesting freshs snapshots from the
>> stats_collector.

> Oh, I see.  Interesting.  Proposals welcome.  I especially dislike the
> ("very_expensive") pgstat check.

Couldn't we simply move that out of the locked stanza?  That is, if no
other worker is working on the table, claim it, and release the lock
immediately.  Then do the "very expensive" check.  If that fails, we
have to re-take the lock to un-claim the table, but that sounds OK.

            regards, tom lane