CPU-intensive actions, such as the sorting of intermediate result sets, can take a considerable length of time. To prevent itself from being blocked during such periods, the SESAM/SQL DBH relocates CPU-intensive actions of this kind in separate tasks provided for service requests.
Service tasks are available for sorting intermediate result sets, for example, but they can also be used for certain utility functions (see the “SQL Reference Manual Part 2: Utilities”). The utility statements COPY, LOAD OFFLINE and UNLOAD OFFLINE are relocated in service tasks; the same applies to parts of utility functions, such as the restoring or updating of a SESAM backup copy, the building of an index, or the reorganization of user data.
A service task is not assigned to a specific type of request; it can carry out all types of service request. This means that it is possible to keep the number of available service tasks low and to make optimum use of them.
At the end of a session, the DBH terminates all the service tasks. Active or incomplete service requests are aborted.
Controlling the utilization of service tasks
System administrators can specify specifically for each session the number of tasks that are to be available at the start of a DBH session and the maximum number of tasks that can be started during the course of the session using the DBH option SERVICE-TASKS. In the linked-in DBH a maximum of one service task is available.
The “SERVICE TASKS” screen in the SESAM/SQL utility SESMON provides system administrators with a means of monitoring service task utilization.
System administrators can use the administration statement MODIFY-SERVICE-TASKS to adjust the number and attributes of the service tasks during ongoing operation.