Choosing the Multi Data Source Algorithm

Before you set up a multi data source, you need to determine the primary purpose of the multi data source—failover or load balancing. You can choose the algorithm that corresponds with your requirements.

Load Balancing

Connection requests to a load-balancing multi data source are served from any data source in the list. The multi data source selects data sources to use to satisfy connection requests using a round-robin scheme. When the multi data source provides a connection, it selects a connection from the data source listed just after the last data source that was used to provide a connection. Multi data sources that use the Load Balancing algorithm also fail over to the next data source in the list if a database connection test fails and the connection cannot be replaced, or if the data source is suspended.

Test Connections on Reserve to Enable Fail-Over

Data sources rely on the Test Reserved Connections (TestConnectionsOnReserve) feature on the data source to know when database connectivity is lost. Testing reserved connections must be enabled for the data sources within the multi data source. WebLogic Server will test each connection before giving it to an application. With the Failover algorithm, the multi data source uses the results from connection test to determine when to fail over to the next data source in the multi data source. After a test failure, the data source attempts to recreate the connection. If that attempt fails, the multi data source fails over to the next data source.

No Fail-Over for In-Use Connections

It is possible for a connection to fail after being reserved, in which case your application must handle the failure. WebLogic Server cannot provide fail-over for connections that fail while being used by an application. Any failure while using a connection requires that the application code close the failed connection, and the transaction must be restarted from the beginning with a new connection.