WebSphere Application Server V7.0: Concepts ... - IBM Redbooks

When there are resource constraints, the WLM component will make sure that
the member processing the higher prioritized requests, gets additional resources
(like CPU), protecting the response time of your most important work.
About WLM changes: The WLM component can change the amount of CPU,
I/O and memory resources assigned to the different operating system
processes (the address spaces). To decide whether or not a process is eligible
for receiving additional resources, the system checks whether or not the
process keeps its defined performance targets, and whether there is more
important work in the system. This technique is performed dynamically so
there is no need for manual interaction after the definitions are made by the
system administrator (the system programmer).
For more information about workload management on the z/OS platform in
combination with WebSphere Application Server for z/OS, refer to 14.1.6,
“Workload management for WebSphere Application Server for z/OS” on
page 428.
High availability
WebSphere Application Server provides a high availability manager service to
eliminate single points of failure in one of the application servers. The high
availability manager service provides failover when servers are not available,
improving application availability. WebSphere Application Server also allows
HTTP Session memory-to-memory replication to replicate session data between
cluster members.
On the z/OS platform the WebSphere Application Server V7.0 high availability
manager can now use native z/OS cluster technology, the cross-system coupling
(XCF) services. This reduces the amount of CPU processsing used for the keep
alive check of clusters, while improving the time it takes to detect a failed
member.
About XCF services: The XCF services allow applications that are located
on multiple z/OS images to communicate with each other as well as to monitor
their status. In the case of WebSphere Application Server for z/OS, the
applications are the various cluster members.
For more information refer to 14.5, “XCF support for WebSphere HA manager”
on page 438.
In a high availability environment, a group of clusters can be defined as a core
group. All of the application servers defined as members of a cluster included in a
core group are automatically members of that core group. The use of core
Chapter 3. WebSphere Application Server concepts 83