– The process monitor performs process recovery when a user process fails. PMON is responsible for cleaning up the cache and freeing resources that the process was using.
– PMON also checks on dispatcher and server processes and restarts them if they have failed.
In general it does the below :
1) Cleans abnormally terminated.
2) Monitoring other background processes.
3) Listener Instance registration.
The DBWn process writes dirty buffers to disk under the following conditions :
– When a server process cannot find a clean reusable buffer after scanning a threshold number of buffers, it signals DBWn to write. DBWn writes dirty buffers to disk asynchronously while performing other processing.
– DBWn periodically writes buffers to advance the checkpoint, which is the position in the redo thread (log) from which instance recovery begins. This log position is determined by the oldest dirty buffer in the buffer cache.