Is SQL*Net message from dblink > 30% a performance issue?
Most likely means that the the shadow process(es) that support the dblink connection(s) are idle. Well they are definitely idle. The only question is are these idle periods between cursors or within an executing cursor. If they are within an executing cursor then whatever is driving the cursor execution, the fetching, is slow. But odds are it's simply an idle dblink connection. See http://kylehailey.com/oracle-sqlnet-wait-events/