Load balancing distributes work across all of the available Oracle RAC database instances. Oracle recommends that applications use connection pools with persistent connections that span the instances that offer a particular service. When using persistent connections, connections are created infrequently and exist for a long duration. Work comes into the system with high frequency, borrows these connections, and exists for a relatively short duration. The load balancing advisory provides advice about how to direct incoming work to the instances that provide the optimal quality of service for that work. This minimizes the need to relocate the work later.
By using the Load Balancing Advisory and run-time connection load balancing goals, feedback is built in to the system. Work is routed to provide the best service times globally, and routing responds gracefully to changing system conditions. In a steady state, the system approaches equilibrium with improved throughput across all of the Oracle RAC instances.
Standard architectures that can use the load balancing advisory include connection load balancing, transaction processing monitors, application servers, connection concentrators, hardware and software load balancers, job schedulers, batch schedulers, and message queuing systems. All of these applications can allocate work.
The load balancing advisory is deployed with key Oracle clients, such as a listener, the JDBC universal connection pool, OCI session pool, Oracle WebLogic Server Active GridLink for Oracle RAC, and the ODP.NET Connection Pools. Third-party applications can also subscribe to load balancing advisory events by using JDBC and Oracle RAC FAN API or by using callbacks with OCI.