check_postgres.pl (--action=autovac_freeze) recently complained that we
needed to run VACUUM FREEZE. Doing so generated a boatload of WAL files -
perhaps on the order of the of the database itself.
Is VACUUM FREEZE something that is normally handled by autovac? If so, how
would we approach finding what caused it not to happen automatically? Or
if it's not, what's the normal approach to scheduling it manually to
prevent this flood of WAL?