When CICS® is initialized, you can switch the CICS monitoring facility on by specifying the system initialization parameter MN=ON. The default setting is MN=OFF. You can also select the classes of monitoring data that you want to be collected using the MNPER, MNEXC, and MNRES system initialization parameters. You can request any combination of performance class, exception class, and transaction resource class data. The class settings can be changed whether monitoring itself is ON or OFF. For more information about the monitoring system initialization parameters, see the CICS System Definition Guide.
When you activate a class of monitoring data, data is collected only for transactions that start thereafter, not transactions already active. You cannot change the classes of monitoring data collected for a transaction after it has started. It is often preferable, particularly for long-running transactions, to start all classes of monitoring data at CICS initialization.