Oracle Networks - PMON Group Processes

• Process Monitor process is background process that periodically scans all processes to find any that have died abnormally. Pmon is then responsible for coordinating cleanup performed by the cleanup main process (CLMN) and the cleanup Slave Process slaves (CLnn).


• Monitors the other background processes and performs process recovery when a server or dispatcher process terminates abnormally


• PMON constantly checks the status of user and database processes. In some cases, failed database processes can be restarted by PMON


• Once instance is started , PMON registers information about the instance to the networklistener


• From Oracle 12c, PMON also registered database services with the listener. This is now handled by the new LREG progress


• PMON normally wakes up every 3 seconds to perform its housekeeping activities. PMON must always be running for an instance


• PMON process is killed then instance will shutdown


• If user process fails,PMON cleans up the database buffer cache and release the resources that the user process was using. It also resets the status of the active transaction table, release locks, and removes the process ID from the list of active processes

The task of detecting abnormal termination remains with PMON. CLMN periodically performs cleanup of terminated processes, terminated sessions, transactions, network connections, idle sessions, detached transactions, and detached network connections that have exceeded their idle timeout.

LREG (Listener Registration) is an Oracle background process created when you start an Oracle 12c or higher database instance. This function was handled by the PMON process in earlier releases.It registers the instance with the listeners.