Fixed Java heap size

With a fixed-size heap, no heap expansion or contraction occurs and this can lead to significant performance gains in some situations. However, using a fixed-size heap is usually not a good idea, because it delays the start of garbage collection until the heap is full, at which point it will be a major task. It also increases the risk of fragmentation, which requires a heap compaction. Therefore, use fixed-size heaps only after proper testing or under the direction of the IBM® support center. Refer to Java Diagnostics Guide (SC34-6650) for more information on heap sizes and garbage collection.

The initial and maximum heap size of a z/OS® Java™ Virtual Machine (JVM) can be set with the -Xms (initial) and -Xmx (maximum) Java command-line options.

In z/OS Explorer, Java command-line options are defined in the _RSE_JAVAOPTS directive of rse.env, as described in "Defining extra Java startup parameters with _RSE_JAVAOPTS" in the Host Configuration Guide (SC27-8437).

#_RSE_JAVAOPTS="$_RSE_JAVAOPTS –Xms128m –Xmx128m"