The Message Service is a separate program used for communication between the elements of a Java cluster.
The Message Service is aware of all the active Java Instances.
The Message Service is responsible for the following tasks in the Java cluster:
· Notification of events that arise in the cluster, for example, if a cluster node gets lost (through failure or shutdown of the instance), or when a service is started or stopped.
· Communication between different services
· Forwarding of messages and requests to all participants (broadcast)
· Prepare logon information for the SAP Web Dispatcher (see Load Balancing Between Many Java Instances)
· Support for Message Server failover
· Guaranteed message transmission
· Exchange of cache information in the cluster
By using the Message Service you can avoid performance problems that occur if all the cluster elements are connected with each other and exchange data with each other. With large clusters especially, this results in considerable performance problems.
The same technology is used as with the SAP Message Server for the earlier AS ABAP versions.
The Message Service is addressed through the Cluster Manager of one of the processes in the Java cluster (dispatcher or server processes), as shown in the figure below.
The settings and the status of the Message Service are made accessible to the administrator via the Message Info Service in the Visual Administrator. For more information, see Message Info Service in the Administration Manual.