V$MTS

Columns
   ___________________________
 
   MAXIMUM_CONNECTIONS
   MAXIMUM_SESSIONS
   SERVERS_STARTED
   SERVERS_TERMINATED
   SERVERS_HIGHWATER

Related:

V$CIRCUIT 
V$DISPATCHER 
V$DISPATCHER_RATE 
V$QUEUE 
V$REQDIST 
V$SHARED_SERVER 
V$THREAD