Setting the memory limits for Java

Java™ applications require more memory than programs written in other languages. You must ensure that CICS® and Java have enough storage and memory available to run Java applications.

About this task

Java uses 24-bit (below-the-line) storage, 31-bit (above-the-line) storage, and 64-bit (above-the-bar) storage. The storage required for the JVM heap comes from the CICS region storage in MVS, and not the CICS DSAs.

Procedure

Ensure that the z/OS® MEMLIMIT parameter is set to a suitable value.
This parameter limits the amount of 64-bit storage that the CICS address space can use. CICS uses the 64-bit version of Java and you must ensure that MEMLIMIT is set to a large enough value for both this and other use of 64-bit storage in the CICS region.
See the following topics:
- Calculating storage requirements for JVM servers
- Estimating and checking MEMLIMIT
Ensure that the REGION parameter on the startup job stream is large enough for Java to run.
Each JVM require some storage below the 16 MB line (24-bit storage) to run applications, including just-in-time compiled code, and working storage to pass parameters to CICS.
For more instructions on estimating and setting the REGION parameter, see Estimating REGION.