SID_XPT listener service in Oracle RDBMS 10g

In Oracle database (10g- 10.2.0) , when an instance registers against the listener, it will also register a service with the name "_XPT" in addition to the normal service names. The service _XPT is intended for use with Data Guard environments for redo transport to the standby instance. You can stop the _XPT service being registered with the listener by using a hidden parameter.

In the init.ora file add the following:

__dg_broker_service_names=''

or in the case of spfile

alter system set "__dg_broker_service_names" = '' scope=spfile;

Please note that this setting begins with two underscore characters. The instance has to be restarted to take effect.

Reference:

How to Stop the sid_XPT Service from Registering with the Listener[Article ID 339940.1]
Diagnosing Connection Problems with an active Data Guard Broker Configuration [Doc ID 745201.1]