CICS region size

The amount of virtual storage for the address space in which CICS® runs is specified by the z/OS® REGION and MEMLIMIT parameters.

  • The z/OS REGION parameter specifies your request for an amount of 24-bit and 31-bit storage, that is, storage below the bar. Up to 2047 MB of storage can be requested, but you must leave enough storage for the region-related services that require MVS storage below 2 GB.
  • The z/OS 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 10 GB. The default value in z/OS for MEMLIMIT is 2 GB.

Reassess your settings for the REGION and MEMLIMIT parameters when you upgrade to a new release of CICS. Also reassess your settings when you install a new release of z/OS or a non-CICS subsystem. Changes in CICS can alter the requirements for 24-bit, 31-bit, and 64-bit storage for the CICS DSAs. Changes to other products can alter the requirements for MVS storage outside the CICS DSAs; for example, the requirements for 24-bit storage might reduce.

You cannot alter the REGION or MEMLIMIT values for the CICS region while CICS is running. You can specify new values on the next start of the CICS region. For instructions, see Setting address space storage limits for a CICS region.

You can specify the REGION parameter in different ways to request a specific amount of storage, or to request all the available 24-bit or 31-bit private storage. The resulting region size below the bar can be unpredictable. The z/OS message IEF374I reports the total amount of storage below the bar that z/OS assigns to a CICS region. The VIRT=nnnK portion of the message shows the 24-bit storage, and the EXT=nnnK portion shows the 31-bit storage. The CICS sample statistics program, DFH0STAT, produces a report that contains this information. You can also use RMF to monitor your use of storage in more detail.

If you plan to increase in the REGION value, remember the following points:
  • Be aware of storage requirements in the high private area in 24-bit and 31-bit storage. Some of this storage is used by the z/OS Communications Server and other programs. An increase in the 24-bit or 31-bit storage allocated to CICS decreases the storage available for the items in the high private area. These items are the local system queue area (LSQA), scheduler work area (SWA), and subpools 229 and 230. A shortage in these subpools can cause S80A, S40D, and S822 abends. For more information about the high private area and LSQAs, see High private area.
  • If you increase the REGION value, remember to increase your values for the CICS system initialization parameters DSALIM and EDSALIM as appropriate, otherwise CICS cannot use the additional storage.
For more information about the REGION and MEMLIMIT parameters and how they apply to z/OS address spaces, see the following z/OS information:

If the total amount of virtual storage required for your CICS regions increases, you might need to review the amount of space allocated for supervisor call (SVC) dumps that are requested by CICS, and the amount of auxiliary storage available. For information about SVC dump data set management, see z/OS MVS Diagnosis: Tools and Service Aids. For information about auxiliary storage management, see the z/OS MVS Initialization and Tuning Guide.