Monitor processing

The JES2 health monitor runs in a separate address space from JES2. There is a corresponding monitor address space for every JES2 address space. The address space name is jes2MON where jes2 is the name of the subsystem that is being monitored. Within the monitor address space, a number of tasks perform the functions needed to determine how the JES2 address space is performing. Use the $JD MONITOR command to display the actual tasks and their current status. This command displays status information on each monitor task and documents the service level of each module that makes up the monitor.

Because most cases of JES2 not responding to requests are caused by the JES2 main task not operating correctly, that is the monitor's primary area of focus. There are some cases where subtasks can cause JES2 to not function properly. Most notable are cases when requests to the security product are not completing in a timely manner. The monitor does not monitor requests made to JES2 subtasks.

The monitor uses cross–memory services to examine data in the JES2 address space. The monitor collects data by sampling values at regular intervals and by extracting data needed to build command responses. This process is designed to have a minimal impact on JES2 operations. However, because the processing is not serialized, it is possible that minor discrepancies could arise in the data it collects and displays. Though rare, this can result in messages that display conditions that could not or did not occur. For example, the monitor collects the current instruction address, PCE address, and exit number in three separate operations. It is possible that the current PCE was in the process of transition and the address does not represent code being run by the exit, or the exit is not one that is used by the PCE. Although the condition that caused the message is valid, and each item of information was valid when collected, the combination of the specific information displayed is not correct. A subsequent $JD STATUS command should provide correct information.