Processing limits for messages in DB/DC and DCCTL environments

To influence the frequency with which scheduling selection occurs, you can set processing limits for messages. These limits set the length of time that application programs wait.

By setting processing limits, you can influence the frequency with which scheduling selection occurs. During the time between each scheduling, processing continues in the message regions. Meanwhile, messages are accumulating in the message queues. As messages accumulate, the interactive effects introduced by new message types and the changing of selection priorities are rearranging the order of waiting transaction codes. Conceivably, while a large queue of messages is being processed, important activity assigned to a high-priority transaction code is waiting.

When the program processes a large queue of messages and updates database segments, other application programs trying to access an updated segment are placed into a wait state. The length of time that the other application programs must wait depends on whether the updating program is processing its queue in multiple- or single-message mode.

To allow controlled reentry to the message scheduling selection process, specify a processing limit count for each transaction code. Each time a scheduled (processing) program requests a new message, the limit count is checked. When the number of requests exceeds the limit count, IMS determines if the region is eligible for quick reschedule.