Trace Listener Dynamic Registration

until 12.1 dynamic registration was controlled by PMON. with 12c LREG (Listener REGistration) background process preform dynamic registration.

LREG

*registers instance information with the listener.
*is a critical background process for each database instance (if it is killed, Oracle goes down).
*does everything PMON used to do and report: service_update, service_register, service_died in the listener.log.

11 to 18 option

From 11.1.0.7 to 18.0, tracing can be enabled using the following command:

alter system set events='immediate trace name listener_registration level 3';

When finished collecting pmon traces,turn this off using:

alter system set events='immediate trace name listener_registration level 0';

19 tracing option

alter system set events 'trace[LREG] disk highest';
alter system set events = 'immediate trace name LREG_STATE level 3';

fo oter releases plese read doc below.

ref:How to Trace Dynamic Registration from PMON or LREG (12c) (Doc ID 787055.1)