Sort with data space

dataspace sorting uses data space to improve the performance of sort applications that use DFSORT's Blockset Technique.

dataspace sorting allows DFSORT to sort large pieces of data at a time. This helps to reduce CPU time and elapsed time.

You can control the maximum size of a data space for a dataspace sorting application with the DSPSIZE parameter. DSPSIZE can direct DFSORT to dynamically determine the maximum size of a data space, subject to the available central storage at the start of the run. DSPSIZE=0 means that DFSORT will not use dataspace sorting.

The actual size of a data space that a dataspace sorting application uses depends upon several factors. See the DSPSIZE description in OPTION control statement for more details.

The following functions and types of data sets are not supported for dataspace sorting:

Spool, dummy, or pipe data set, or z/OS UNIX file, as input.
User exits
INREC, OUTFIL, OUTREC, and SUM
EQUCOUNT

Dataspace sorting is seldom used for very small data sets of a few MB or so because it is more efficient to sort small amounts of data entirely in main storage.

The following are actions you can take that might increase the use of dataspace sorting:

Specify sufficient main storage. The default is 6MB, the recommended minimum for dataspace sorting. If you increase the amount of main storage specified, more dataspace sorting is possible, especially when sorting large amounts of data (multiple hundred MBs). Specifying more than 12MB or so will have no significant impact on DFSORT's decision to use dataspace sorting; it will, however, improve the performance of large non-dataspace sorting applications.
Specify generous extent sizes for work data sets, especially for secondary extents. Dataspace sorting is frequently used in conjunction with disk work space but never with Hiperspace or with tape work data sets.
Specify DSPSIZE=MAX.
Verify that IEFUSI does not place any restrictions on the size of the data spaces a single address space can create.
Ensure that DFSORT has accurate information about the input file size. DFSORT can automatically estimate the file size for disk input data sets and tape data sets managed by DFSMSrmm or a tape management system that uses ICETPEX. See File size and dynamic allocation for information on situations where DFSORT cannot determine the file size accurately, and what to do about it.