High private area

The area at the high end of the address space is not specifically used by CICS®, but contains information and control blocks that the operating system needs to support the region and its requirements.

The high private area consists of four areas:
  • LSQA
  • SWA
  • Subpool 229
  • Subpool 230

The usual size of the high private area varies with the number of job control statements, messages to the system log, and number of opened data sets.

The total space used in this area is reported in the IEF374I message in the field labeled SYS=nnnnK at jobstep termination. A second SYS=nnnnK is issued, which refers to the high private area above 16 MB. This information is also reported in the sample statistics program, DFH0STAT.

You cannot reduce the size of this area, except possibly subpool 229. This subpool is where the z/OS® Communications Server stores inbound messages when CICS does not have an open receive issued to the z/OS Communications Server. To determine whether this is happening, use CICS statistics (see SNA statistics) obtained following CICS shutdown. Compare the maximum number of RPLs that are posted in the shutdown statistics with the RAPOOL value in the SIT. If these values are equal, subpool 229 is probably being used to stage messages, and the RAPOOL value should be increased.

In some situations, the way in which the storage in the high private area is used might cause an S80A abend. There are at least two considerations:
  • The use of MVS™ subpools 229 and 230 by access methods such as SNA.

    SNA and VSAM might find insufficient storage for a request for subpools 229 and 230. Their requests are conditional and so should not cause an S80A abend of the job step (for example, CICS).

  • The MVS operating system itself, relative to use of LSQA and SWA storage during job-step initiation.

    The MVS initiator's use of LSQA and SWA storage can vary, depending on whether CICS was started using an MVS START command, or started as a job step as part of already existing initiator and address space. Starting CICS with an MVS START command is better to minimize fragmentation in the space above the region boundary. If CICS is a job step initiated in a previously started initiator's address space, the way in which LSQA and SWA storage is allocated might reduce the apparently available virtual storage because of increased fragmentation.

Storage above the region boundary must be available for use by the MVS initiator (LSQA and SWA) and the access method (subpools 229 and 230).

Consider initiating CICS using an MVS START command, to minimize fragmentation of the space above your specified region size. The more effective use of the available storage might avoid S80A abends.

Your choice of sizes for the MVS nucleus, MVS common system area, and CICS region influences the amount of storage available for LSQA, SWA, and subpools 229 and 230. It is unlikely that the sizes and boundaries for the MVS nucleus and common system area can be changed easily. To create more space for the LSQA, SWA, and subpools 229 and 230, you might need to decrease the region size.

For more information about subpools and managing private storage allocation, see Virtual storage management in z/OS MVS Programming: Authorized Assembler Services Guide.