Oracle Net Multiplexing Configuration

Oracle Net Configuration Assistant enables you to configure network service names for clients. Oracle Universal Installer launches Oracle Net Configuration Assistant after software installation. The configuration varies depending on the installation mode.

1. Administrator or runtime installation: Oracle Net Configuration Assistant prompts you to configure network service names in the tnsnames.ora file to connect to an Oracle Database service.
2. Custom installation: Oracle Net Configuration Assistant prompts you to select naming methods to use. If local is selected, then Oracle Net Configuration Assistant prompts you to configure network service names in the tnsnames.ora file to connect to an Oracle Database service.

• Nomenclature for the Listener
  The nomenclature for the Listener remains largely the same across Oracle versions, including 8, 11g R2, and 19c. The core concept and name persist. Here's a breakdown and clarification:
  

  • LISTENER: This is the primary name and it remains consistent. You'll still configure and manage something called the "Listener." It's the process that listens for incoming client connection requests.
  • listener.ora: This is the configuration file for the Listener. The filename itself doesn't change. The contents of listener.ora will have version-specific parameters and settings, but the file itself is still named listener.ora.
  • LSNRCTL: This is the Listener Control utility. You use lsnrctl (pronounced "listener control") to start, stop, check the status of, and otherwise manage the Listener. This utility name is consistent across all mentioned versions. lsnrctl start, lsnrctl status, lsnrctl stop are all common commands.
  • Default Listener Name: While you can name your Listener anything you want (and it's common to have multiple Listeners in more complex environments), the default Listener name is, and has historically been, simply LISTENER (all caps). If you don't explicitly specify a name during configuration, Oracle will often default to this. This default name is consistent across versions.
  • Oracle Net Listener (or Oracle Net Services Listener): Sometimes you might see it referred to more formally as the "Oracle Net Listener" or "Oracle Net Services Listener". This is just a more descriptive name, referring to the fact that the Listener is part of Oracle's networking layer (Oracle Net Services). It's not a different name for the Listener process, just a more complete description.
  • Local Listener versus Grid Infrastructure Listener: In Real Application Clusters (RAC) environments, you'll encounter a slightly more nuanced situation. You'll still have "Listeners," but you have two main types:
    • Local Listener: This runs on each node of the RAC cluster and typically handles connections to instances on that specific node. The name may follow the default 'LISTENER', but you may name it something different.
    • SCAN Listener (Single Client Access Name): This is a cluster-wide concept. The SCAN provides a single name for clients to connect to the entire RAC cluster, regardless of which specific node they need to reach. The SCAN Listener(s) (there are usually three for redundancy) handle these connections and redirect them to the appropriate Local Listener. The SCAN Listener will have its own name defined in the cluster. The config files are typically managed by the grid infrastructure.

In Summary The fundamental name "LISTENER" doesn't change between Oracle 8, 11g R2, and 19c. The utility `lsnrctl` and the configuration file `listener.ora` are also consistent. The key differences are in the *configuration options* available within `listener.ora` and the presence of SCAN Listeners in RAC environments. The main point of confusion would arise if you consider RAC, and the two type of listeners (SCAN vs Local). However, even the *Local* Listener is still, conceptually and practically a listener that follows the naming of `LISTENER`.
The following section discusses connection pooling.

The tnsnames.ora file that configures the Network Services listener to use Connect Manager and multiplexing should look something like this:

#E:\ORACLE\ORA81\NETWORK\ADMIN\TNSNAMES.ORA 
  Configuration File:E:\Oracle\Ora81\NETWORK\ADMIN\
     tnsnames.ora
# Generated by Oracle Network Services Assistant
PETS_ATLANTA =
  (DESCRIPTION =
    (SOURCE_ROUTE=YES)
    (ADDRESS_LIST =
      (ADDRESS = 
       (PROTOCOL = TCP)
       (HOST = ATLANTA.EPETS.COM)
       (PORT = 1630))
      (ADDRESS = 
      (PROTOCOL = TCP)
       (HOST = ATLANTA.EPETS.COM)
       (PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = HOUSEOPETS)
    )
  ) 

The next lesson covers connection pooling.

[1]Multiplexing: Combining several individual transmissions and sending them across a single connection to and from a database.