I wrote:
> Perhaps it is worth adding a defense to autovac to not believe last
> autovac times that are in the future, since the system clock is not
> under our control and could go backwards. Other than that I don't
> think there's any bug here.
Oh, the other thing that comes to mind is that it's a bad move not
to have exposed last_autovac_time anywhere in the pgstat views.
Obviously we cannot back-patch that, but I think it should be fixed
going forward. This whole thing might've been much less of a mystery
if that state had been visible.
regards, tom lane