This section contains the following subsections:
9.3.1 Overview of Run-Time Connection Load Balancing
In an Oracle Real Application Clusters environment, a connection could belong to any instance that provides the relevant service. In the best case, all instances perform equally well and randomly retrieving a connection from the cache is appropriate. However, when one instance performs better than others, random selection of a connection is inefficient. The run-time connection load balancing feature enables routing of work requests to an instance that offers the best performance, minimizing the need to relocate work.
UCP JDBC connection pools leverage the load balancing functionality provided by an Oracle RAC database. Run-time connection load balancing requires the use of an Oracle JDBC driver and an Oracle RAC database.
Run-time connection load balancing is useful when:
Traditional balancing of workload is not optimal
Requests must be routed to make optimal use of resources in a clustered database
Capacity within the cluster differs and is expected to change over time
The need to avoid sending work to slow, hung, and dead nodes is required
UCP uses the Oracle RAC Load Balancing Advisory. The advisory is used to balance work across Oracle RAC instances and is used to determine which instances offer the best performance. Applications transparently receive connections from instances that offer the best performance. Connection requests are quickly diverted from instances that have slowed, are not responding, or that have failed.
Manages pooled connections for high performance and scalability
Receives continuous recommendations on the percentage of work to route to database instances
Adjusts distribution of work based on different back-end node capacities such as CPU capacity or response time
Reacts quickly to changes in cluster reconfiguration, application workload, overworked nodes, or hangs
Receives metrics from the Oracle RAC Load Balance Advisory. Connections to well performing instances are used most often. New and unused connections to under-performing instances will gravitate away over time. When distribution metrics are not received, connection are selected using a random choice.
9.3.2 Setting Up Run-Time Connection Load Balancing
In addition, you must configure the Oracle RAC Load Balancing Advisory with service-level goals for each service for which load balancing is enabled:
The service goal must be set to one of the following:
The service goal can be set using the
goalparameter, and the connection balancing goal can be set using the
The connection balancing goal must be set to
SHORT. For example,
EXECUTE DBMS_SERVICE.MODIFY_SERVICE (service_name => 'sjob' -, goal => DBMS_SERVICE.GOAL_THROUGHPUT -, clb_goal => DBMS_SERVICE.CLB_GOAL_SHORT);
EXECUTE DBMS_SERVICE.MODIFY_SERVICE (service_name => 'sjob' -, goal => DBMS_SERVICE.GOAL_SERVICE_TIME -, clb_goal => DBMS_SERVICE.CLB_GOAL_SHORT);
The connection balancing goal can also be set by calling the
You can set the connection balancing goal to
LONG. However, this is mostly useful for closed workloads, that is, when the rate of completing work is equal to the rate of starting new work.