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listener [Oracle NET]
When a client wants to establish a connection to an Oracle Server, it usually first contacts the listener. The listener then creates a foreground process (dedicated mode) or attaches the request to an exising foreground process (shared mode).
The client then directly communicates with that foreground process.
A listener can accept requests for more than one instance. Likewise, more than one listeners can accept requests for the same instance (load balancing).
Service registration is a mechanism in which PMON registers information with the listener. This allows the listener to determine which dispatcher can best handle a client connection.
The listener must be configured with the following things:
This is a typical listener.ora file. lsnrctl uses per default listener for listener_name, so use listener there as well, unless some very important reasons require differently.
listener_name = (ADDRESS_LIST = (ADDRESS = (PROTOCOL=TCP) (HOST=laptop) (PORT=1521) ) ) SID_LIST_listener_name = (SID_LIST= (SID_DESC= (SID_NAME=adpdb) (ORACLE_HOME=/home/oracle/OraHome1) ) )
Restricting clients on specific nodes from connecting to the listener