SYS1.PARMLIB(BPXPRMxx)

Some of the SYS1.PARMLIB(BPXPRMxx) settings affect shared classes performance. Using the wrong settings can stop shared classes from working. These settings might also have performance implications. For further information about performance implications and use of these parameters, refer to MVS Initialization and Tuning Reference (SA22-7592) and UNIX System Services Planning (GA22-7800). The most significant BPXPRMxx parameters that affect the operation of shared classes are the following:
  • MAXSHAREPAGES, IPCSHMSPAGES, IPCSHMMPAGES and IPCSHMNSEGS

    These settings affect the amount of shared memory pages available to the JVM. The shared page size for a 31-bit z/OS® UNIX system service is fixed at 4 KB. Shared classes try to create a 16 MB cache by default. Therefore set IPCSHMMPAGES greater than 4096.

    If you set a cache size using -Xscmx, the JVM will round up the value to the nearest megabyte. You must take this into account when setting IPCSHMMPAGES on your system.

  • IPCSEMNIDS and IPCSEMNSEMS

    These settings affect the amount of semaphores available to UNIX processes. Shared classes use IPC semaphores to communicate between the JVMs.