JCL conversion for single address space job processing

The single address space job processing method (AS1) is similar to the standard procedure method because no JCL procedure member is written to a PROCLIB.

Instead, the information to run each CA group is stored as a member of HPCACTL in a format to be used for dynamic allocation.

Because each CA group is run as a subtask within the IMS HP Change Accumulation Utility control address space, restrictions apply to the format of the JCLOUT, and therefore to the underlying DBRC skeleton JCL.

One-step execution of PGM=DFSUCUM0 is allowed only for any one CA group. Therefore, the GENJCL VOLNUM() cannot be used. All steps other than PGM=DFSUCUM0 are ignored.

All selected CA groups must have the same EXEC PARM= value and the same allocations for the following DD names:
  • STEPLIB
  • DFSRESLB
  • IMSDALIB
  • RECON1
  • RECON2
  • RECON3
  • IMS (see Note 1)
  • DFSHDBSC (see Note 2)
Notes:
  1. Required when IMS management of ACBs is not enabled.
  2. Required when IMS management of ACBs is enabled, IMS catalog data sets are not registered in the DBRC, and DFSMDA member is not present.
These conditions are required because the parameter and DD allocations are performed once for the IMS HP Change Accumulation Utility control address space and reused by each CA subtask.

The DD names SYSIN, SYSPRINT, SORTWKnn, HPCADUMY, HPCMSGDD, ICBUCUMN, DFSUCUMN, DFSUCUMO, and DFSULOG are renamed, and separate copies are allocated for each subtask. All other DD names are ignored. All other JCL restrictions of the standard procedure method apply equally to JCL for AS1 mode.

The number of parallel subtasks is set by using the parallel sort count. Because a single address space is used, contention exists for the limited resources, particularly 24-bit memory. IMS HP Change Accumulation Utility in AS1 mode computes and reports a default value for the number of parallel subtasks that can be supported for a typical environment. When the parallel sorts count is omitted or set to a value that is greater than the calculated default, the default value is used.

The true maximum number of subtasks might be less than the default if, for example, your setup includes a large number of logs, CA groups, and DBDs. Other factors, such as DFSORT replacements, system exits routines, or user exit routines, can also affect how memory is allocated.

Another consideration is the number of DD allocations that can be supported in a single address space. The limiting value depends on the number of DDs and the unit count for each DD. The task input output table (TIOT) size and number of DDs is described in the "ALLOCxx" section in the z/OS® MVS™ Initialization and Tuning Reference.

The most critical factor for this condition is the SORTWKnn statements, either coded in the JCL or assumed by dynamic allocation. When work files (limit is 256 per sort) are large, the TIOT can be exceeded in as few as three concurrent sort steps.

The following information summarizes the steps for AS1:

ISPF (Setup option 1, JCL job statements)
Either enter HPCSTASK in the Member field, or clear both the Member and PROCLIB. Clearing both of these fields results in HPCTASK being used.
Two-step batch
Include the PROC=HPCSTASK parameter in the EXEC PARM value.
Extended batch
  1. Omit the STC= parameter and command.
  2. Do one of the following:
    • Include the PROC=HPCSTASK parameter or the Procedure Name = HPCSTASK command.
    • Omit the STC=, PROC=, and DD HPCAPROC (this will default to PROC=HPCSTASK).
Restriction: When you use single address space job processing, HPCSTASK is a reserved keyword.