How DFSORT uses data space

The recommended setting for DSPSIZE is MAX. This enables DFSORT to dynamically determine the size of a data space to be used for data space sorting, taking into account the size of the file being sorted and the central storage usage activity of the system. DFSORT has full control over total data space sorting activity, and sites can customize their definition of DSPSIZE=MAX with the installation options EXPMAX, EXPOLD, and EXPRES. DSPSIZE=n and DSPSIZE=p% should be reserved for use as a run-time override for applications that have a special reason to limit the size of a data space for data space sorting.

The amount of data space storage used for each sort job is displayed in message ICE188I. DFSORT dynamically determines how best to use data spaces for each particular run:

If the input data set size is known to be small enough so that the sort can be accomplished in main storage, no data space is created.
If the size of the input data set in relation to the maximum available data space amount is too large, no data space is created. Dataspace sorting is only used if the size of the data space that could be created is large enough to improve the performance of the sort application.
If the size of the input data set in relation to the total available main storage is too large, no data space is created. To ensure that you have enough main storage to use dataspace sorting, follow the recommended virtual storage guidelines for DFSORT (Table 1).

In general, DFSORT takes into account the effect on the application's performance and the effect on the system's performance before using data space. If either effect is not desirable, DFSORT chooses not to use dataspace sorting.

See Memory object sorting, hipersorting and data space sorting for information about the benefits and operation of dataspace sorting, and Hipersorting, memory object sorting, and data space sorting for additional information on using data space sorting effectively.