TELL ME HOW MANY BACKGROUND PROCESSES HELP ORACLE INSTANCE TO RUN?

SMON

The System Monitor carries out a crash recovery when a crashed instance is started up again. It also cleans temporary segments. SMON checks the SCN in all datafile headers when the database is started. Everything is OK if all of these SCNs matches the SCN found in the controlfile. If the SCNs don't match, the database is in an inconsistent state. SCN Number is the System Change Number provided by Oracle for each committed transaction. When the database in inconsistent state while the database is opened, crash recovery is done. Crash recovery is the recovery of a database in a single-instance configuration or an Oracle Real Application Clusters configuration in which all instances have crashed. In contrast, instance recovery is the recovery of one failed instance by a live instance in an Oracle Real Application Clusters configuration.

SMON_SCN_TIME is the metadata table populated for every five minutes by SMON

If column_tracking_level is set to 1 SMON also updates sys.col_usage$ another metadata table.

PMON

The Process Monitor checks if a user process fails and if so, do all cleaning up of resources that the user process has acquired. In the case of shared server configuration, PMON checks dispatchers and server processes and restarts them if they have failed. It also does another important thing. During service registration, PMON provides the listener with Names of the database services provided by the database. However, if there is no listener at startup, PMON can obviously not register those information. Therefore, PMON tries then periodically to register with the listener, which might take up to 60 seconds. There is a command to force the registration using