Finding the right logging level

Hi list !

I have change my PostrgreS configuration to log messages to 
windows' eventlog. There were way too many events logged, so I 
changed to level to :
log_min_messages = warning
I have still a lot of events log though ! Every one minute, I have 
a "autovacuum: processing database "postgres"" event.
This does not really sound like a warning to me...
Did I change the wrong setting, or should I raise the log level 
even higher ?

Thanks for your help !

Regards
--
Arnaud