Assigning the BDCAS and TDCAS to the SYSSTC service class

We recommend that you assign the batch dump capture address space (BDCAS) and the transaction dump capture address space (TDCAS) to the SYSSTC service class. They control dump capture for batch and CICS abends, and do not use any resources except when capturing an Abend-AID report. When an abend occurs, the task that is running in the abending address space waits until the BDCAS or TDCAS has finished capturing information for the Abend-AID report. If the BDCAS or TDCAS has a lower dispatching priority than the abending address space, the delay can be excessive.

The Workload Manager component (WLM) of z/OS assigns each job to a service class based upon the WLM policy in effect for that system. Each service class is assigned a performance goal and importance level that WLM uses to manage system resources. WLM periodically adjusts dispatching priorities as needed to make sure that the most important workloads meet their goals. When a system uses nearly all available CPU, the address spaces with the lowest dispatching priority sometimes receive very little service. Under these conditions, if the BDCAS or TDCAS has a low dispatching priority, the abending jobs or CICS transactions might be delayed because they are waiting for the BDCAS or TDCAS to complete their processing.

The only practical way to ensure that the BDCAS and TDCAS have a sufficiently high dispatching priority to service abending batch jobs and CICS transactions is to assign the BDCAS and TDCAS to service class SYSSTC. Address spaces assigned to SYSSTC have a fixed dispatching priority of 254 (X'FE'). The address spaces that are assigned to service class SYSTEM have a higher dispatching priority of 255 (X'FF'). All other address spaces have a lower dispatching priority. Workload Manager manages them to meet the service class goals.

Hence, the active Workload Manager policy should assign the BDCAS and TDCAS to the SYSSTC service class to make sure that the BDCAS and TDCAS have a high enough dispatching priority for dump capture to complete quickly.