Workload manager

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The workload manager (WLM) is an integral part of the z / OS mainframe operating system from IBM . It is the component that controls access to the resources for work on az / OS . It also provides data that can be used to distribute the load within a parallel sysplex .

properties

Prioritized access to operating resources is necessary on a mainframe computer, since many different applications use the computer at the same time and resources must be distributed according to customer requirements. The workload manager is therefore the central component that guarantees a reliable execution time of work units under z / OS and thus enables a basic requirement for reliable access to database systems.

WLM controls the allocation of resources on the basis of service classes (in the technical term: service classes ). Units of work are assigned to the service classes via a classification mechanism. The classification is carried out by the system administrator of the z / OS system and can be carried out using attributes that exist for the program products under z / OS; for example, user name, transaction name , transaction classes or program names, which are used in the applications. The administrator also defines a target for the service classes. The target can include the average response time of the units of work running in the class, a percentage of the units of work that should end in a certain time, or a throughput-based target. The target that can be assigned to a service class depends on how much information the workload manager receives about the applications. In addition to the target, each service class is assigned an importance that defines which classes should be preferred or disadvantaged if the resources in the system are no longer sufficiently available.

WLM uses a control mechanism to control access to the resources at runtime. For this purpose, data is continuously collected from the z / OS system. This is information about the waiting states of the work units for the resources, the number of current work units and their processing times. The information is grouped into service classes according to the classification made by the system administrator. Then, on the basis of this information, target achievement is calculated for each class and, if necessary, access to the resources is adjusted. The adjustment always takes place depending on the importance of the classes and the degree to which the target is missed. That is, the most important class that is furthest off target is considered first, and the least important classes are the potential candidates to deliver resources. In this case, however, will consider in determining whether a potential donor ( donor ) actually uses the equipment needed. This control mechanism runs every 10 seconds in z / OS, and in the meantime the data is collected for the next calculation interval. A calculation interval ends when an adjustment in favor of a service class can be carried out.

WLM controls the access to the processors and I / O units of the system, the access to the memory and the provision of address spaces to allow programs for certain applications to be processed. Access to the processors is regulated , for example, via dispatch priorities . For this purpose, all work units of a service class are assigned the same priority, although the assignment of this priority does not have to correspond in every case to the definition of the importance of the service class. Rather, it is based on the current workload of the system, the requirements of the class and the achievement of objectives. This behavior of the z / OS-WLM is also called target-oriented workload management, and it is an important differentiation criterion from proportion-oriented workload management, in which fixed access to the operating resources is assigned. The latter is often found in workload management components of Unix systems.

The second essential difference between the z / OS WLM and other workload management components is the strong integration with the applications and program products that run under a z / OS operating system. The constant communication between the WLM and these applications makes it possible to recognize the transactions of the applications and to control them in the system through the WLM. To date, this has not been possible on any other system in which any control is limited to processes.

In addition to controlling a system, the z / OS WLM offers a number of interfaces that allow load balancing components to receive information from the system so that work can be intelligently distributed to one or more z / OS systems. Several z / OS systems can be interconnected in a parallel sysplex , and this combination is also supported in order to present a uniform image to the outside world. z / OS WLM also has a number of other functions that support load balancing on a physical system between multiple logical systems and control access to large disk farms depending on the work to be accessed.

literature

  • Michael Teuffel, Robert Vaupel: The z / OS operating system and the zSeries. Oldenbourg Verlag Munich, 2004, ISBN 3-486-27528-3
  • Paola Bari et al .: System Programmer's Guide to: Workload Management. IBM Redbook, SG24-6472

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