Using cluster configurations

The capability to spread workload among appservers using clustering can be a valuable asset in configuring highly scalable production environments. This is especially true when the application is experiencing bottlenecks that are preventing full CPU utilization of Symmetric Multiprocessing (SMP) servers. When adjusting the WebSphere system queues in clustered configurations, remember that when a server is added to a cluster, the server downstream receives twice the load. This is illustrated in Figure 19-7.

Figure 19-7 Clustering and queuing

Two Web containers within a cluster are located between a Web server and a data source. It is assumed the Web server, Web container, and data source (but not the database) are all running on a single SMP server. Given these constraints, the following queue considerations need to be made: Web server queue settings can be doubled to ensure ample work is distributed to each Web container. Web container thread pools can be reduced to avoid saturating a system resource such as CPU or another resource that the servlets are using. The data source pools can be reduced to avoid saturating the database server. Java heap parameters can be reduced for each instance of the appserver. For versions of the JVM shipped with WAS, it is crucial that the heap from all JVMs remain in physical memory. Therefore, if a cluster of four JVMs are running on a system, enough physical memory must be available for all four heaps.

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IBM is a trademark of the IBM Corporation in the United States, other countries, or both.