13.2 Understanding Connection Load Balancing

The connection load balancing feature improves connection performance by balancing the number of active connections among multiple dispatchers.

In an Oracle Real Application Clusters (Oracle RAC) environment, connection load balancing can also balance the number of active connections among multiple instances.

Because the Listener Registration (LREG) process can register with remote listeners, a listener can always be aware of all instances and dispatchers, regardless of their location. Depending on the load information, a listener decides which instance and, if shared server is configured, which dispatcher to send the incoming client request.

In a shared server configuration, a listener selects a dispatcher in the following order:

1. Least loaded node.

2. Least loaded instance.

3. Least loaded dispatcher for that instance.

In a dedicated server configuration, a listener selects an instance in the following order:

1. Least loaded node.

2. Least loaded instance.

Load Balancing across nodes for HTTP presentation is introduced in this release. The remote listener can load balance across instances that are on different nodes for HTTP presentation using HTTP redirect.

An Oracle RAC environment requires that the dispatchers on each instance be cross-registered with the other listeners on the other nodes. This is achieved by the use of the LISTENER attribute of the DISPATCHERS parameter.

Note:

For optimum connection load balancing results, the instances that belong to the same database service should be on equivalent hardware and software configurations.

• Example of Connection Load Balancing for Shared Server Configuration
  
• Example of Connection Load Balancing for Dedicated Server Configuration
  
• COLOCATION_TAG of Client Connections
  The COLOCATION_TAG parameter is an alphanumeric string that you can use with the CONNECT_DATA parameter of the TNS connect string.

See Also:

• "Registering Information with a Remote Listener" for additional information about cross-registration

• Oracle Database Reference for complete information about the SERVICE_NAMES and INSTANCE_NAME parameters

• Configuring a Shared Server Architecture for additional information about the LISTENER attribute

• Oracle Database Global Data Services Concepts and Administration Guide for information about management of global services