frecuencia autovacuum

Hola, estoy tratando de hacer funcionar el nuevo demonio autovacuum,
pero por alguna razon se esta corriendo con demasiada frecuenciam, los
parametros en postgresql.conf son los siguientes (practicamente los
default):

#---------------------------------------------------------------------------
# AUTOVACUUM PARAMETERS
#---------------------------------------------------------------------------

autovacuum = on # enable autovacuum subprocess?
#autovacuum_naptime = 60 # time between autovacuum runs,
in secs
#autovacuum_vacuum_threshold = 1000 # min # of tuple updates before
# vacuum
#autovacuum_analyze_threshold = 500 # min # of tuple updates before
# analyze
#autovacuum_vacuum_scale_factor = 0.4 # fraction of rel size before
# vacuum
#autovacuum_analyze_scale_factor = 0.2 # fraction of rel size before
# analyze
#autovacuum_vacuum_cost_delay = -1 # default vacuum cost delay for
# autovac, -1 means use
# vacuum_cost_delay
#autovacuum_vacuum_cost_limit = -1 # default vacuum cost limit for
# autovac, -1 means use
# vacuum_cost_limit

y en el log me aparece:

2006-03-27 15:17:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:18:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:19:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:20:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:21:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:22:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:23:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:24:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:25:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:26:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:27:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:28:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:29:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:30:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:31:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:32:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:33:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:34:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:35:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:36:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:37:00 CST LOG: autovacuum: processing database "radius"
2006-03-27 15:38:00 CST LOG: autovacuum: processing database "postgres"
2006-03-27 15:39:00 CST LOG: autovacuum: processing database "radius"

este es un servidor de prueba, no tiene ninguna actividad, esta recien
instalado,
cual prodria ser el problema?

atte