From
http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html#avd ...
There is a little known module in PostgreSQL contrib directory called as pgavd. It works in conjunction with statistics collector. It periodically connects to a database and checks if it has done enough operations since the last check. If yes, it will vacuum the database.
Essentially it will vacuum the database when it needs it. It would get rid of playing with cron settings for vacuum frequency. It should result in better database performance by eliminating overdue vacuum issues.
