Grouping JES3 Job Classes

The GROUP initialization statement defines the resources available to a group of JES3 job classes. A maximum of 255 groups can be defined. The system programmer specifies whether jobs in the group will run under JES-managed initiators or WLM-managed initiators as specified on the MODE= parameter.

The EXRESC parameter defines the execution resources (initiators and devices) dedicated to the group, and also defines the systems where jobs in the group will run. Devices assigned to the group satisfy requests for mountable volumes (not permanently resident) from jobs within the group. The EXRESC parameter should be repeated for each processor's execution resources. If the execution resource requirements are the same for all processors, the EXRESC parameter can be specified once on the GROUP statement with a processor name of *ALL.

The EXRESC parameter also defines the initiator allocation and deallocation options (see Starting and Stopping Initiators). For WLM-managed job class groups, the initiator related options (that is, the number of initiators and allocaiotn and deallocation options) can be specified, but they will be ignored. If the job class group is later modified so that JES initiator management is used, the initiator related options will take effect.

The BAR parameter on the GROUP statement specifies a job priority used as a barrier to the generalized main scheduling process; it determines when no more jobs should be scheduled on an associated processor. Within a job class group, no jobs with priorities lower than the barrier are run until all jobs with priorities higher than the barrier have run. BAR can limit job scheduling because of processing requirements (such as, a job that cannot obtain sufficient storage on a processor or a job that is incompatible with the current job mix under a best-mix scheduling algorithm). If BAR=PRTY is specified, the priority of the first job that cannot be scheduled is the barrier value. BAR=16, the default, means that there is no priority barrier for the group.

Note: A class can be assigned to a new job class group with the *MODIFY,C=cls,GROUP=grp command. This is useful if you have multiple job classes assigned to a group and you want to test WLM initiator management for one of the classes in the group. You can use the *MODIFY,C=cls command to switch one of the job classes to a WLM-managed job class group without changing initiator management for the other classes in the group.