Setting address space storage limits for a CICS region

When you submit your CICS job, set the z/OS parameters REGION and MEMLIMIT to specify the amount of virtual storage for the address space in which CICS runs.

About this task

You cannot alter the REGION and MEMLIMIT values for the CICS® region while CICS is running. You can specify new values only when you start the CICS region.

The REGION parameter specifies your request for an amount of 24-bit and 31-bit storage, that is, storage below the bar, for the CICS address space. Up to 2047 MB of storage can be requested, but you must leave enough storage below the bar for the system region in 24-bit storage, and items in the high private area such as the local system queue area (LSQA). You can specify the REGION parameter in different ways to request a specific amount of storage, or all the available 24-bit or 31-bit private storage. The resulting region size below the bar can be unpredictable.

The MEMLIMIT parameter specifies the limit of 64-bit (above-the-bar) storage for the CICS region. A CICS region needs a MEMLIMIT value of at least 6 GB. The default value in z/OS® for MEMLIMIT is 2 GB.

Procedure

  1. Calculate the amount of 24-bit (below-the-line) storage and 31-bit (above-the-line) storage to request on the REGION parameter.
    See Estimating and setting REGION.
  2. Specify a suitable REGION parameter for the CICS region.
    You can set REGION in the following ways:
    • You can specify the REGION parameter in the JOB statement in the CICS JCL. In this situation, each step of the job runs in the requested amount of space.
    • You can specify the REGION parameter in the EXEC statement (program execution line) for CICS. In this situation, each step runs in its own amount of space. Use the EXEC statement instead of the JOB statement if different steps need greatly different amounts of space. For example, use the EXEC statement if you are using extra job steps to print auxiliary trace data sets after CICS has shut down (as in the DFHIVPOL installation verification procedure).
    • The z/OS installation exit IEFUSI can limit the REGION value that you specify. For information about IEFUSI, see IEFUSI - Step Initiation Exit in z/OS MVS Installation Exits.
    For further details about specifying the REGION parameter, and information about the amount of storage that z/OS allocates in response to your request, see REGION Parameter in the z/OS MVS JCL Reference.
  3. Calculate the amount of 64-bit (above-the-bar) storage that you need to specify with the MEMLIMIT parameter.
    This amount depends on the facilities that you plan to use. See Estimating, checking, and setting MEMLIMIT.
  4. Identify the MEMLIMIT value that applies to your CICS region, and change it if necessary.
    You can set MEMLIMIT in the following ways:
    • A MEMLIMIT value can be specified in the JOB statement in the CICS JCL, or in the EXEC statement (program execution line) for CICS.
    • If there is no MEMLIMIT value specific to the CICS region, the MEMLIMIT value that is set in the z/OS SMFPRMxx PARMLIB member, or the system default, applies.
    • The z/OS installation exit IEFUSI can override any other MEMLIMIT values.
    The following example shows a MEMLIMIT value set in the program execution line:
    //CICS EXEC PGM=DFHSIP,PARM='SI',REGION=0M,MEMLIMIT=6G
    For further details about changing a MEMLIMIT value in z/OS, or determining the value that applies to the CICS region that you are setting up, see Limiting the use of memory objects in the z/OS MVS Programming: Extended Addressability Guide.