Central storage

DFSORT leverages central storage as intermediate work space through the use of either memory objects or Hiperspaces. Using the installation defaults of HIPRMAX=OPTIMAL, MOSIZE=MAX and MOWRK=YES ensures that DFSORT will use memory object or Hiperspace whenever possible. Sites can tune their definition of HIPRMAX=OPTIMAL and MOSIZE=MAX through use of the EXPMAX, EXPOLD, EXPRES and TUNE installation options. See z/OS DFSORT Installation and Customization for more information.

DFSORT’s use of memory object or Hiperspace storage depends upon the availability of central storage, the needs of other concurrent memory object sorting, Hipersorting, and dataspace sorting applications throughout the time the application runs, and the settings of the EXPMAX, EXPOLD, EXPRES and TUNE installation options. Consequently, it is possible for the same application to use varying amounts of memory object or Hiperspace storage from run to run. If enough memory object or Hiperspace storage is available, DFSORT uses it exclusively for intermediate storage. If the amount of available storage is insufficient, DFSORT uses a combination of work data sets with Hiperspace or memory object storage, or even work data sets alone.

DFSORT's use of memory object and Hiperspace storage is very dynamic; multiple concurrent sort applications always know each other's storage needs and never try to back their memory objects or Hiperspaces with the same portion of storage. In addition, DFSORT checks the available storage prior to creating each memory object or Hiperspace. Depending on the TUNE installation default each SORT application can be more or less dynamic:

by checking available storage once and then allocating all available storage expected to be used at initialization, or
by checking available storage multiple times and allocating it in increments throughout the run.

DFSORT also has the capability of switching from using memory objects or Hiperspaces to using disk work data sets when either of the following occur:

allocation of an additional memory object or Hiperspace is likely to cause a storage shortage (for more information on how DFSORT uses central storage, see “Recommendations” under “Hipersorting, Memory Object Sorting, and Data Space Sorting” in z/OS DFSORT Tuning Guide).
the total Hipersorting, memory object sorting, and dataspace sorting activity on the system reaches the limits set by the EXPMAX, EXPOLD, and EXPRES installation options.

Memory object and Hipersorting requires that work data sets be available, as well as central storage. DFSORT forces the use of dynamic allocation for memory object sorting or Hipersorting if work data sets are not requested explicitly. For further details, see the MOSIZE , MOWRK and HIPRMAX options of the OPTION control statement.