Run-time options and performance

Table 1 shows run-time options that influence the performance of DFSORT, a description of each option, any restrictions, the IBM-supplied installation default value and a possible reason for modifying that value at run-time. Any IBM-supplied installation default value can be changed to a different site installation default value using ICEPRMxx members in PARMLIB or the ICEMAC macro.

Table 1. Run-time Options That Influence DFSORT Performance
Run-time Option	Description	Restriction	IBM-supplied Default Value and Reason for Modifying
SIZE and MAINSIZE	Upper limit for total storage above and below 16 MB virtual.	Limited by TMAXLIM or MAXLIM when SIZE=MAX or MAINSIZE=MAX is in effect.	The default is MAX. Modify when sorting unusually large data sets.
DSA	Upper limit for dynamically adjusted storage.	Only used when SIZE=MAX or MAINSIZE=MAX is in effect and DFSORT can determine that performance will benefit.	The default is 64 MB. Set to a lower value if you do not want DFSORT to adjust storage up to 64 MB.
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.	The default is 4 KB. Modify when sufficient REGION is specified but application terminates for lack of below 16 MB virtual storage.
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.	The default is 0.
ARESALL	Storage above 16 MB virtual that is reserved for system use.	Can reduce the amount of virtual storage available for use by DFSORT.	The default is 0.
ARESINV	Storage above 16 MB virtual that is reserved for use by an invoking program.	Only used when DFSORT is program-invoked.	The default is 0.
HIPRMAX	Upper limit for Hiperspace for a single application.	Hiperspaces limited by IEFUSI installation exit.	The default is OPTIMAL. Set to 0 to disable Hipersorting.
DSPSIZE	Upper limit for data space size.	Data spaces limited by IEFUSI.	The default is MAX. Set to 0 to disable dataspace sorting.
MOSIZE	Maximum size of a memory object for a single application.	Memory objects limited by MEMLIMIT JCL and IEFUSI installation exit.	The default is MAX. Set to 0 to disable memory object sorting.
MOWRK and NOMOWRK	Whether memory objects can be used as intermediate work storage.	NOMOWRK can cause an increase in CPU time.	The default is MOWRK. Use NOMOWRK only when necessary
DYNALLOC	Requests dynamic allocation and specifies device type and number of work data sets.		The default is (SYSDA, 4). The unit name can be changed to a name used exclusively by DFSORT to isolate work data set volumes from the general pool of devices.
DYNAPCT	Default additional work data sets (as percentage) to be dynamically allocated.	Allocated with zero space and only used when needed.	The default is 10. Increase if failures due to insufficient work space are a concern. If set to OLD, additional work data sets are not allocated.
DYNSPC	Default amount of space to allocate for dynamically allocated work data sets.	Only used when DFSORT cannot determine the input file size.	The default is 256 MB. Set to a higher value to allow larger sorts when DFSORT cannot determine the file size.
CINV and NOCINV	Whether control interval access is used for VSAM input data sets.	Improves performance for VSAM input data sets.	The default is CINV.
CFW and NOCFW	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.	The default is CFW. Use NOCFW for large sorts.
EQUALS and NOEQUALS	Whether input order is preserved for records with equal keys.	Can cause an increase in CPU time.	The default is VLBLKSET. Use NOEQUALS whenever possible.
VERIFY and NOVERIFY	Whether output records are checked for correct order.	Can cause an increase in CPU time.	The default is NOVERIFY. Use VERIFY only when necessary.
ALTSEQ	Whether a collating sequence other than EBCDIC is used.	Can cause an increase in CPU time.	There is no default value. Use ALTSEQ only when necessary.
AVGRLEN	Specifies the average input record length in bytes for variable-length sort applications.	This value is used when necessary to determine the input file size. The resulting value is important for sort applications, since it is used for several internal optimizations as well as for dynamic work data set allocation (see OPTION DYNALLOC).	There is no default value. Using a value close to the actual average record length may improve variable-length record sort performance.
FILSZ	Specifies either the exact number of records to be sorted or an estimate of the number of records to be sorted.	The type of value specified can have a significant effect on performance and work data set allocation. See File size for more information.	There is no default value. Using a value close to the actual file size may improve sort performance when message ICE118I is received.
ODMAXBF	The maximum buffer space to be used for each OUTFIL data set.	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.	The default is 2 MB. When you are running OUTFIL applications with a large number of output data sets and constrained storage, use a smaller value to reduce total virtual storage usage.
NOBLKSET	Controls the use of Blockset techniques.	If necessary, DFSORT can still use non-Blockset techniques for other reasons. Using non-Blockset techniques significantly degrades performance.	There is no default value. Specify NOBLKSET only temporarily to bypass a Blockset problem.
CHALT and NOCHALT	Specifies whether ALTSEQ is to be applied to character format fields (CH).	As with ALTSEQ, can cause an increase in CPU time.	The default is NOCHALT. Use CHALT only when necessary.
COBEXIT	Specifies the library for COBOL E15 and E35 routines.	COBEXIT=COB1 is obsolete.	The default is COB2. Use COB1 only if necessary for compatibility.
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.	The default is NONE. Use an EFS program 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.	The default is NONE. Use LOCALE processing only when necessary for your application.

See z/OS DFSORT Application Programming Guide for a complete list of run-time override options.