Installation options and performance

Table 1 shows site-wide installation options that influence the performance of DFSORT, a description of each option, and additional comments about the option.

Table 1. Installation Options That Influence DFSORT Performance
Type	Installation Option	Description	Comments
Options that tailor main storage	SIZE	Upper limit for total storage above and below 16 MB virtual	Limited by TMAXLIM when SIZE=MAX is in effect. The recommended value is MAX.
	OVERRGN	Upper limit for storage over and above that specified by REGION.	Limited by the IEFUSI or IEALIMIT installation-wide exits using the "region limit" values.
	MAXLIM	Upper limit for storage below 16 MB virtual.	Always used. The recommended value is 1 MB.
	TMAXLIM	Upper limit for total storage above and below 16 MB virtual.	Only used when SIZE=MAX or MAINSIZE=MAX is in effect. The recommended value is 6 MB.
	DSA	Upper limit for dynamic storage adjustment.	Only used when SIZE=MAX or MAINSIZE=MAX is in effect and the use of additional storage should improve performance. The recommended value is 64 MB.
	MINLIM	Lower limit for SIZE or MAINSIZE.	Only used when SIZE=n or MAINSIZE=n is less than MINLIM. The recommended value is 440 KB.
	RESALL	Storage below 16 MB virtual that is reserved for system use.	Only used when SIZE=MAX or MAINSIZE=MAX is in effect. Can reduce the amount of virtual storage available for use by DFSORT.
	RESINV	Storage below 16 MB virtual that is reserved for use by an invoking program.	Only used when SIZE=MAX or MAINSIZE=MAX is in effect and DFSORT is program-invoked.
	ARESALL	Storage above 16 MB virtual that is reserved for system use.	Can reduce the amount of virtual storage available for use by DFSORT.
	ARESINV	Storage above 16 MB virtual that is reserved for use by an invoking program.	Only used when DFSORT is program-invoked.
Options that affect use of Hiperspace, memory objects and data space	HIPRMAX	Upper limit for Hiperspace for a single application.	Hiperspaces limited by IEFUSI installation exit. Recommended setting is OPTIMAL. Use EXPMAX, EXPOLD, and EXPRES to control Hipersorting on a system-wide basis.
	MOSIZE	Upper limit for a memory object for a single application.	Recommended setting is MAX. Memory objects are limited by IEFUSI and JCL MEMLIMIT. If central storage is overcommitted, set MOSIZE to a low value and test it. If resource contention is a problem only at specific times, set MOSIZE to MAX in your environment installation modules and use a time-of-day installation module to restrict the MOSIZE value for all jobs during those specific times.
	MOWRK	Whether memory objects can be used as intermediate work storage or only as an extension of main storage.	Recommended setting is YES. DFSORT’s use of memory objects as work space provides more efficient operation and improved balancing of central storage resources across concurrent sort applications.
	DSPSIZE	Upper limit for data space size.	Recommended setting is MAX. If central storage is overcommitted, set DSPSIZE to a low value and test it. If resource contention is a problem only at specific times, set DSPSIZE to MAX in your environment installation modules and use a time-of-day installation module to restrict the DSPSIZE value for all jobs during those specific times. Data spaces are limited by IEFUSI.
	EXPMAX	Upper limit for total available central storage used for all Hipersorting, memory object and data space sorting activity.	Available central storage is subject to non-Hipersorting, non-memory object and non-data space sorting activity. Should be set to MAX unless you want to limit Hipersorting, memory object and data space sorting activity to a fixed portion of storage.
	EXPOLD	Upper limit for total old expanded and central storage used for all Hipersorting, memory object and data space sorting activity.	Old expanded and central storage are subject to non-Hipersorting, non-memory object and non-data space sorting activity. Should be set to 50% unless a large migration of old storage data causes a problem at your site.
	EXPRES	Lower limit for available expanded and central storage reserved for non-Hipersorting and non-memory object sorting use.	Available expanded and central storage are subject to non-Hipersorting and non-memory object sorting activity. Should be set to 10% unless you want DFSORT to have lower access priority to storage than other applications.
Options that influence allocation of work data sets	DYNAUTO	Whether work data sets should be dynamically allocated automatically.	Set to YES, or to IGNWKDD if you want to use dynamic allocation even when JCL work data sets are specified. Can cause an increase in CPU time for small sort applications but helps minimize the amount of disk space required for sorting.
	DYNALOC	Default device type and number of work data sets when dynamic allocation is requested.	Does not request dynamic allocation; only supplies defaults.
	DYNAPCT	Default additional work data sets (as percentage) to be dynamically allocated and used only when needed.	If set to OLD, additional data sets are only allocated when DFSORT cannot determine the input file size. Exceptions are documented in z/OS DFSORT Installation and Customization
	DYNSPC	Default amount of space to allocate for dynamically allocated work data sets.	Only used when DFSORT cannot determine the input file size.
	IDRCPCT	Compaction ratio to use for IDRC-compacted tape data sets when computing data set size.	Tells DFSORT how much work space to dynamically allocate when input is on an IDRC-compacted tape and DFSORT cannot determine the input file size.
	VIO	Whether VIO work data sets should be automatically reallocated to real disk locations.	ACS routines can override this option.
Options that affect VSAM performance	CINV	Whether control interval access is used for VSAM input data sets.	Improves performance for VSAM input data sets.
Options that affect VSAM performance	VSAMBSP	Amount of VSAM buffer space to use.	To improve VSAM performance, set OPTIMAL or MAX.
Options that affect input and output data set performance	IOMAXBF	The maximum buffer space to be used for disk SORTIN and SORTOUT data sets.	Recommended setting is 34 MB. Should only be lowered when device contention or long channel connect times are a problem. Lowering the default could result in larger EXCP counts for these data sets, but could also decrease the channel connect time per EXCP.
Options that affect input and output data set performance	ODMAXBF	The maximum buffer space to be used for each OUTFIL data set.	Recommended setting is 2 MB. Lowering the value can cause performance degradation for the application. When you use more than 2 MB, the performance improvements are small except for EXCPs, and, there is an increased need for storage.
Other options that affect performance	CFW	Whether cache fast write is used for DFSORT work data sets.	Only applicable for work data sets located on disks attached to cached 3990 storage control units. Can be used only if DFSORT SVC is installed. Cache fast write can reduce the elapsed time of sorting applications. CFW is more beneficial to DFSORT performance for small and intermediate sized sorts, where the work data sets are relatively small.
	EQUALS	Whether input order is preserved for records with equal keys.	Can cause an increase in CPU time. The default setting of VLBLKSET should be changed to NO if possible.
	VERIFY	Whether output records are checked for correct order.	Can cause an increase in CPU time.
	ALTSEQ	Whether a collating sequence other than EBCDIC is used.	Can cause an increase in CPU time.
	SDB and SDBMSG	Whether system-determined block size is used for output data sets whose block size is zero.	Use of optimum block sizes for output data sets provides more efficient performance than using other block sizes.
	IGNCKPT	Specifies whether Checkpoint/Restart requests at run-time should be ignored.	When CKPT is specified, the Blockset technique cannot be selected. Therefore, the recommended setting is YES so that the Blockset technique can be used.
	CHALT	Specifies whether ALTSEQ is to be applied to character format fields (CH).	As with ALTSEQ, can cause an increase in CPU time. Recommended setting is NO.
	COBEXIT	Specifies the library for COBOL E15 and E35 routines.	Use COB2. COB1 is obsolete.
	EFS	Specifies the name of a user-written Extended Function Support program to be called by DFSORT.	Can cause an increase in CPU time and elapsed time. Use only when necessary for your application.
	LOCALE	Specifies whether locale processing is to be used and, if so, designates the active locale.	Should only be used when required since it can show degraded performance relative to collation using character encoding values.

See z/OS DFSORT Installation and Customization for a complete list of site-wide installation options and the z/OS DFSORT Application Programming Guide for corresponding run-time overrides.