The default value for autovacuum_vacuum_cost_delay of 20 ms is a medium one appropriate for a smaller system. If you have a busy server, you can easily discover that autovacuum never quite keeps up with incoming traffic. Particularly if you have a system that's capable of good I/O performance, you can drop this setting significantly in order to give autovacuum more opportunities to keep pace with your server.
Large servers will commonly run with a cost delay in the 1 ms to 5 ms range. Your first response to not having autovacuum run often enough to keep up should be to reduce this parameter until you've reached that range. As OS timers sometimes won't delay for less than 10 ms at a time, at some point you ...
