Limitations

The maximum amount of Hiperspace used by DFSORT is limited to the minimum of the following values:

The IEFUSI exit limit on the total amount of Hiperspace and data space that can be allocated in a single job step. See z/OS MVS Installation Exits for a description of IEFUSI.
The HIPRMAX value in effect, when set to a value other than OPTIMAL. The HIPRMAX value in effect is either the installation default, an overriding value specified at run-time, or an overriding value specified in the installation ICEIEXIT routine. Note that the value specified in the ICEIEXIT routine overrides any other value.
Available storage. Throughout the run, DFSORT determines the pages available on the system, subtracts from this the amount of storage needed by other concurrent Hipersorting applications, and factors in the values specified for installation options EXPMAX, EXPOLD, and EXPRES. If as a result of any such check, either a storage shortage is predicted or one of the site limits for total storage usage by all Hipersorting applications is reached, DFSORT switches from using Hiperspace to using disk work data sets for all currently running Hipersorting applications.
In addition, all future DFSORT applications are prevented from using Hipersorting until the storage situation is relieved. This prevents Hipersorting applications by themselves from causing excessive paging.

Since this last criteria depends very heavily on system activity, especially other concurrent Hipersorting and memory object sorting activity, DFSORT applications can use varying amounts of Hiperspace when run at different times and under different conditions. In fact, it is possible for such applications to not use any Hiperspace.

The following are those cases for which you should not attempt to adjust your application; in these cases the best performance for the individual job and for the system is achieved by not using Hipersorting:

Other performance features are in use. Hipersorting is not used when DFSORT decides to use dataspace or memory object sorting. DFSORT dynamically chooses between using dataspace sorting, memory object sorting and Hipersorting; DFSORT selects the one that provides the best performance for the particular sort. Messages ICE188I and ICE199I indicate whether dataspace sorting or memory object sorting was used for a particular run.
The size of the input data set is very small. If the amount of data to be sorted is known to be small enough that the sort can be accomplished in main memory, Hipersorting is not used. Since no intermediate data is generated, neither Hiperspace nor disk work data sets are needed. The presence of message ICE080I indicates that a sort was processed in main memory.