Task lists of the administrative task scheduler

The administrative task scheduler manages tasks that are defined by users and stores them in two redundant task lists. As a result, the administrative task scheduler can continue working even if one task list is unavailable.

The two task lists are the Db2 table SYSIBM.ADMIN_TASKS and the VSAM data set that is indicated in the data definition ADMTDD1 of the started task of the administrative task scheduler. The administrative task scheduler maintains the consistency between the two task lists.

The Db2 task list SYSIBM.ADMIN_TASKS is accessed through a connection to the Db2 subsystem that is identified in the DB2SSID parameter of the started task of the administrative task scheduler.

The administrative task scheduler works and updates both task lists redundantly, and remains operable so long as at least one of the task lists is available. Therefore, the administrative task scheduler continues working when Db2 is offline. If a task list becomes unavailable, the administrative task scheduler continues to update the task list. When both task lists are available again, the administrative task scheduler automatically synchronizes them.

The SYSIBM.ADMIN_TASKS_HIST table is a history table that stores the status and execution output of the tasks that are in the SYSIBM.ADMIN_TASKS table. The administrative task scheduler manages the SYSIBM.ADMIN_TASKS_HIST table simultaneously to the task lists that are in the SYSIBM.ADMIN_TASKS table and the VSAM data set.

If the SYSIBM.ADMIN_TASKS_HIST table is not accessible (for example, if the Db2 subsystem is down), the output of previous executions are not available to the DSNADM.ADMIN_TASK_OUTPUT user-defined function. However, even if the SYSIBM.ADMIN_TASKS_HIST table is not accessible, the last five execution statuses are available to the DSNADM.ADMIN_TASK_STATUS user-defined function. The status and output of previous executions are stored in the task list until they can be copied to the SYSIBM.ADMIN_TASKS_HIST table.

To prevent the SYSIBM.ADMIN_TASKS_HIST table from containing too many status entries, the administrative task scheduler limits the number of status entries per task that are stored. This limit is specified by the MAXHIST parameter. This parameter is a positive integer with a default value of 10. When the limit is reached, the oldest status entries are deleted. You can specify this parameter in the started task when the administrative task scheduler starts, or you can modify this parameter dynamically by using the MODIFY console command.