ORACLE 12C : Listener service registration

With previous releases PMON (Process Monitor) was responsible for registering database services to the Listener.
Starting from Oracle 12C there is a change in architecture with respect to the service registration in Oracle
Database Release 12c.
Oracle has introduced a new mandatory background process dedicated for “database service registration to the Listener” and named LREG (Listener Registration Process).
The listener registration process (LREG) registers information about the database instance and dispatcher processes with the Oracle Net listener (see “The Oracle Net Listener”).
When an instance starts, LREG polls the listener to determine whether it is running. If the listener is running, then LREG passes it relevant parameters. If it is not running, then LREG periodically attempts to contact it.
You can also use the remote_listener parameter ti instruct LREG to register a service with a remote listener (which is common in Oracle RAC environments).
To trace the service registration to Listener, I have enabled tracing (by following the same old method used with PMON) as follows.
SQL> alter system set events = ‘immediate trace name
listener_registration level 3’;
SQL> alter system register;
This would dump the service registration trace in the LREG trace file under the
background dump destination as shown below.
SQL> show parameter background_dump_desp
—————————— ——— ——————————————
Background_dump_dest string /app/oracle/diag/orcl/orcl/trace

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