The JES2 print/punch processor, the external writer, the network SYSOUT transmitter and spool offload SYSOUT transmitter can select only data sets which already have output groups constructed.Varying the number of output groups, (JOENUM parameter on the OUTDEF initialization statement) influences the processing of output.

Specifying many output groups makes more work available for selection within the configuration; however, the increased number of output groups also increases the size of the checkpoint data set thus adversely affecting performance.

An output group that does not yet describe a unit of work is a “free” JOE. When the building of output groups for a job depletes the number of available free JOEs, the job or spin data waits until more output groups become available.

The JES2 output processor builds output groups for a job without making a distinction as to whether the routing of the data sets is for the local node or for some other node. JES2 makes the distinction when it adds the output groups to the output queues; JES2 then places all the output groups for the local node on one of the class queues, and places all the others on the network queue.