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WAS V6 introduces a new default messaging provider. See Chapter 12, "Using and optimizing the default messaging provider" of the redbook IBM WebSphere V6 Scalability and Performance Handbook, SG24-6392 for details.
On z/OS, the messaging engine (ME) runs inside a separate address space, called the Control Region Adjunct (CRA). See Figure 8-2. A resource adapter in the CRA is responsible for taking a messaging request and sending it to a message dispatcher (RA dispatcher) in a servant region, where the MDB is really dispatched. This resource adapter supports transaction commit and rollback. Messages in MEs can be persisted in a database for recovery.
CRA is a special type of servant region. It is started by Workload Manager for z/OS. When a CRA fails within a server, WLM on z/OS restarts the CRA. Meanwhile the messaging engine in the failed CRA is moved to another server in the cluster and JMS connections are subsequently routed to that ME. Depending on the configuration, the ME is then moved back to the original server's CRA when it is restarted or stays in the CRA. Thus, WLM on z/OS and HAManager complement each other.
