Configuring the IBM WebSphere Application Server

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The DayTrader benchmark application runs are conducted with a few adapted IBM WebSphere Application Server (WAS) parameters, such as larger pool sizes (for example, ORB pool, WebContainer pool, JMS thread pool).

A more significant change is the increase in the Java™ heap size for the application server. The memory for the WAS server is sized large enough to allow a Java heap size which is larger than the default size. A larger Java heap size can help busy applications to fulfill specific user demands. But a Java heap sized too large for the available server memory may cause swapping out memory to disk. This can have the opposite effect and slow down the system performance.

The Java heap size can be changed for each defined application server individually in WAS server profiles using the administration console as follows:

WAS admin console path: Exemplary set the Java heap to 2 GB for the application server in the SUT

Application servers > server1 > Process definition > Java Virtual Machine

Initial heap size: 2048 MB
Maximum heap size: 2048 MB

Note: Setting the initial heap size and the maximum heap size to the same size reduces the overhead of memory allocation operations on the Java heap during application runtime. However, that should be done in production environments only, when the Java heap requirements for the application servers are well understood. For benchmark applications this was done to provide stable throughput conditions.