30.3. MDB and Consumer pool size

Most application servers, including JBoss, allow you to configure how many MDBs there are in a pool. It is important to understand that the MaxPoolSize parameter in the ejb3-interceptors-aop.xml file will not have an effect on how many sessions or consumers are created because the Resource Adaptor implementation is not aware of the application server MDB implementation.
For example, if you set the MDB MaxPoolSize to 1, 15 sessions or consumers are created (15 is the default). To limit how many sessions or consumers are created, set the maxSession parameter on the resource adapter, or through an ActivationConfigProperty annotation on the MDB. 
@MessageDriven(name = "MDBMessageSendTxExample",
  activationConfig =
    {
      @ActivationConfigProperty
        (propertyName = "destinationType", propertyValue = "javax.jms.Queue"),
      @ActivationConfigProperty
        (propertyName = "destination", propertyValue = "queue/testQueue"),
      @ActivationConfigProperty
        (propertyName = "maxSession", propertyValue = "1")
    })
@TransactionManagement(value= TransactionManagementType.CONTAINER)
@TransactionAttribute(value= TransactionAttributeType.REQUIRED)
public class MyMDB implements MessageListener
{ ....}