Failover Scenarios When Using a RAC Database

An application that uses an RAC database must handle database failover scenarios. The MDB run time does not fail over to the newly available database. To enable failover, the deployment descriptors dequeue-retry-count and dequeue-retry-interval must be specified in orion-ejb-jar.xml file. The first parameter, dequeue-retry-count, tells the container how many times to retry the database connection in case a failure happens; the default is 0. The second parameter, dequeue-retry-interval, tells the container how long to wait between attempts (to accommodate for the time it takes for database failover); the default value is 60 (seconds).

Note: The RAC-enabled attribute of a data source is discussed in Data Sources chapter in the Oracle Application Server Containers for J2EE Services Guide.(RAC is real application clusters. For more information on using this flag with an infrastructure database, see The Oracle9iAS High Availability Guide.)

These parameters are attributes of the <message-driven-deployment> element, as shown in the following example:

<message-driven-deployment name="MessageBeanTpc"
   connection-factory-location=
     "java:comp/resource/cartojms1/TopicConnectionFactories/aqTcf"
   destination-location=
     "java:comp/resource/cartojms1/Topics/topic1"
   subscription-name="MDBSUB"
   dequeue-retry-count=3
   dequeue-retry-interval=90/>

A standalone OJMS client running against an RAC database must write similar code to obtain the connection again, by invoking the API DbUtil.oracleFatalError(), to determine if the connection object is invalid. It must then reestablish the database connection if necessary. The following example outlines the logic:

getMessage(QueueSesssion session)
{
    try
    {
        QueueReceiver rcvr;
         Message msgRec = null;
        QueueReceiver rcvr = session.createReceiver(rcvrQueue);
         msgRec = rcvr.receive();
    }
    catch(Exception e )
    {
        if (exc instanceof JMSException)
        {
           JMSException  jmsexc = (JMSException) exc;
           sql_ex = (SQLException)(jmsexc.getLinkedException());

           db_conn =
             (oracle.jms.AQjmsSession)session.getDBConnection();

           if ((DbUtil.oracleFatalError(sql_ex, db_conn))
           {
               // failover logic
            }
          }
     }
}