Memory object sorting

Memory object sorting is a DFSORT capability that uses memory objects in 64-bit virtual storage. For a more detailed description of this capability, see Memory object sorting, hipersorting and data space sorting. The sections that follow include information on how to use memory object sorting in the most efficient way at your site.

DFSORT selects the most appropriate mode (memory objects as intermediate work space or memory objects as additional main storage) for each particular run. Not every sort application can use memory object sorting, and even for those sorts that can use memory object sorting, it may be more advantageous not to use it under certain circumstances.

A memory object, used in memory object sorting, is allocated in virtual storage above the bar and backed by central storage. The use of central storage for memory object sorting must always be weighed against the possibility of degrading performance for a particular job, or for the entire system, by overusing central storage. If DFSORT were to use memory object sorting indiscriminately, there could be a significant increase in paging activity and a resulting reduction in total system performance, affecting all jobs, including sorts.

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

The number of megabytes used for a memory object during the sort is displayed in message ICE199I or ICE299I depending on whether DFSORT uses it as intermediate work space or as an extension to main storage. If memory object sorting is not used, both messages show a value of 0M.