SERV_MOD_ACT_TRACE_ENABLE problem SQL&gt; EXECUTIVE DBMS_MONITOR.SERV_MOD_ACT_TRACE_ENABLE(service_name=&gt;'ACC_SRV',waits=&gt;TRUE,binds=&gt;FALSE,instance_name=&gt;'inst1');


Why this function need instance_name parameter?
I think the relations between instance and service are as follows(http://docs.oracle.com/cd/B19306_01/network.102/b14212/concepts.htm):


One Service for one instance
multi-services for one instance


If I call SERV_MOD_ACT_TRACE_ENABLE, a single trace file is created for each session that uses the ACC_SRV service. What effect is this instance parameter which is not null?
There is no need for the instance name, as you can see in the documentation


  This procedure will enable SQL tracing for a given combination of
  Service Name, MODULE and ACTION globally unless an instance_name is
  specified.


instance_name has a default value null implicating it is not a required parameter. In a RAC database this would just enable tracing for your service in all open instances.