Heap limitations: Increase the Java heap to its maximum

One of the key factors affecting large object processing is the maximum size of the Java heap.

IBM® Business Process Manager for z/OS® by default uses a 64-bit JVM. On 64-bit systems, the available address space is practically unlimited, so the heap size is usually limited only by available physical memory. As always, ensure that sufficient physical memory is available to support the maximum JVM heap size and native memory requirements, plus the memory requirements of other processes.

For 31-bit JVMs, the Java 6 JVM supports heaps up to approximately 1.2 GB in size.

Tip: Since the 2 GB address space allowed by the 31-bit system is shared with other z/OS resources, the actual limit of the heap size depends on memory usage by resources such as thread stacks, JIT compiled code, loaded classes, shared libraries, and buffers used by OS system services. An extremely large heap limits address space available for other resources and can cause runtime failures.

This topic applies only to the z/OS platform For more information about heap setting techniques, see the Network Deployment (z/OS), Version 8.0 > Tuning performance documentation in the WebSphere® Application Server Information Center.

This topic applies only to the Distributed platforms For more information about heap setting techniques, go to the WebSphere Application Server Information Center and search for Tuning the JVM in the Distributed operating systems, Version 8.0 documentation.