Fixing short-on-storage conditions caused by subpool storage fragmentation

You might experience short-on-storage conditions in 24-bit storage or 31-bit storage despite increasing the DSALIM or EDSALIM limits, respectively. In this situation, you might need to enable the CICS® self-tuning mechanism. It is also possible to fix the size of each individual DSA by using the corresponding SIT override.

About this task

Use the self-tuning mechanism and the SIT overrides only if increasing the DSALIM or EDSALIM limit does not completely resolve the short-on-storage problems.

Allocating into managed extents can result in a block of storage in an extent that is insufficient to satisfy a GETMAIN request. With the dynamic nature of the subpools and DSAs, this situation will probably resolve as the extent storage is reused. If you specify the initial DSA size using the SIT override for the affected DSA, CICS reserves contiguous extents up to the amount specified, and eliminates the blocks of storage.

Tip: Define MAPS as MAPS. If you defining MAPS as programs, they are loaded into LDRES rather than into LDNUC. LDRES is part of the SDSA and is more sensitive to fragmentation.

Procedure

  1. You can add records to the local catalog to enable the CICS self-tuning mechanism for storage manager domain subpools.
    For details of how to manipulate subpool records using the CICS-supplied utility program, DFHSMUTL, see Local catalog storage program (DFHSMUTL) .
  2. You can fix the size of one or more individual DSAs by using the corresponding SIT overrides (CDSASZE, UDSASZE, SDSASZE, RDSASZE, ECDSASZE, EUDSASZE, ESDSASZE, and ERDSASZE).
    For more information about these overrides, see System initialization parameter descriptions and summary .
    To determine the values to use, follow this process:
    1. Collect DFH0STAT output for information showing storage use by each DSA during the intervals.
    2. Review the CICS statistics for several days.
      The statistics provide information that you can use to define the amount of storage used at a subpool and a DSA level. Extent usage is shown with the number of extents added and released.
      In addition to the DSA information provided in DFH0STAT, the results about each subpool are provided, including the DSA where it was allocated. If statistics are being gathered, end-of-day statistics only provide data since the last statistics collection.