When you are starting CICS®, you switch the monitoring facility on by specifying the system initialization parameter MN=ON. MN=OFF is the default setting. You can select the classes of monitoring data you want to be collected using the MNPER, MNRES, and MNEXC system initialization parameters. You can request the collection of any combination of performance class data, transaction resource class data, and exception class data. You can change the class settings whether monitoring facility is ON or OFF. For details of all the system initialization parameters that control monitoring activities, see the CICS System Definition Guide.
When CICS is running, you can control the monitoring facility dynamically. Just as at CICS initialization, you can switch monitoring on or off, and you can change the classes of monitoring data that are being collected. There are two ways of doing this:
If you activate a class of monitoring data in the middle of a run, the data for that class becomes available only for transactions that are started thereafter. 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.