Selecting work to maximize efficiency

To minimize contention for output devices, JES2 allows the installation to define work selection criteria that can be specific for each output device (local and remote printers and punches and offload devices). The work selection criteria on the respective device initialization statements create the following definitions:
  • Specification of job and output characteristics that JES2 considers when selecting work for an output device
  • Order of importance (priority) of the selection characteristics
  • Characteristics of the printer and job that must match exactly.

JES2 initializes the setup characteristics of a device based on the specifications supplied on a device (printer/punch) initialization statement.

A job's output is grouped based on the data sets' output requirements. These requirements are defined by the job submitter with the job's job control language (JCL) or by JES2-supplied defaults.

When selecting work to be processed on a device, JES2 compares the device's characteristics to the output requirements associated with the pieces of work awaiting processing. In addition, JES2 compares each piece of work against all others to determine the best match for the device. If work output requirements are found that match a device's characteristics, JES2 sends the output associated with that piece of work to that output device. If a piece of work and an output device cannot be paired, the work will not be selected for output until the operator changes the output device specifications or the output requirements for the piece of work.

Work selection control provides efficient use of output devices by allowing them to print or punch specified output classes without requiring continual operator intervention of setup characteristics such as forms or print trains (the piece of hardware that carries the print type). Also, when too much work is adversely affecting system performance, the system programmer or operator can specify work to be offloaded (that is, moved off the work queues and temporarily out of contention for system resources. See Offloading work and backing up the system for an explanation of offloading.)