5.1 About Service Registration

The listener determines whether a database service and its service handlers are available through service registration. During registration, the Listener Registration (LREG) process provides the listener with information about the following:

• Names of the database services provided by the database

• Name of the database instance associated with the services and its current and maximum load

• Service handlers (dispatchers and dedicated servers) available for the instance, including their type, protocol addresses, and current and maximum load

The preceding information enables the listener to direct a client request appropriately.

The following figure shows two database instances registering information with two listeners. The figure does not represent all the information that can be registered. For example, listening endpoints, such as the port numbers, can be dynamically registered with the listener.

Figure 5-2 Service Registration

Description of "Figure 5-2 Service Registration"

If the listener is not running when an instance starts, then the LREG process cannot register the service information. LREG attempts to connect to the listener periodically, but it may take up to 60 seconds before LREG registers with the listener after it has been started. To initiate service registration immediately after the listener is started, use the SQL statement ALTER SYSTEM REGISTER. This statement is especially useful in high availability configurations.