JES3 Basics

JES2 processing is considered to be independently controlled. Each JES2 image processes its own job input, job scheduling and job output. JES2 uses a contention-based paradigm for managing a multi-image workload. Each image “wakes up” periodically and attempts to serialize the JES2 checkpoint using a hardware serialization technique.

The image that succeeds carries out job and output scheduling activities. The others go back “to sleep” waiting for another chance. There is no cooperative decision-making process. The order in which activities occur and on which images is random.

 By contrast, JES3 processing is considered to be centrally controlled. One image is designated as the focal point for the entry and distribution of jobs and for the control of resources needed by the jobs.

That image, called the global processor, distributes work to itself and the other images in the configuration, known as local processors. It is from the global processor that JES3 manages jobs and resources for the entire JESplex, matching jobs with available resources.