Workload Manager
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 resources for the work on z / OS. It also provides data that can be used for load balancing within a Parallel Sysplex.
Properties
On a mainframe, a prioritized access to resources is necessary because many different applications use the computer at a time and must be a customized appropriate allocation of resources. The workload manager is thus the central component, which guarantees reliable execution time of work units under z / OS, enabling a prerequisite for reliable access to database systems.
WLM controls the resource allocation on the basis of service classes ( the technical term: Service Classes). Work units are grouped into classes of service via a classification mechanism. The classification is performed by the system administrator of the z / OS system and can be made on the basis of attributes that exist for the program products on z / OS; for example, user name, transaction name, transaction classes or program names that are used in the applications. As another of the administrator defines a target for the service classes. The target can the average response time of units of work that run in the class include, representing a percentage of the units of work that are formed in a specific time, or a throughput- oriented specification. What is the goal for a service class can be assigned depends on how much information the workload manager receives the applications. In addition to the objective of each service class is assigned an importance that determines which classes are to be preferred or disadvantaged if the resources are no longer available in the system sufficiently available.
WLM uses a control mechanism to control access to resources at runtime. These continuous data from the z / OS system are collected. This is information about the wait states of the units of work on the equipment, the number of running units of work and their processing times. The information is summarized into service classes according to the classification that was made by the system administrator. Then, the target performance of the access to resources is based on this information calculated for each class and, if necessary, adjusted. The adaptation is always a function of the importance of the classes and the degree in which the target is missed. That is, the most important class that has the most missed their given target is considered as the first and the classes with the lowest importance are the potential candidates to deliver resources. It is, however, considered whether a potential donor (donor) actually uses the equipment needed. This control mechanism takes place every 10 seconds in the z / OS, and in the meantime, the data for the next computing interval are collected. A calculation interval ends when an adjustment for the benefit of a service class may be carried out.
WLM controls access to the processors and I / O units in the system, the access to the memory, and the provision of address spaces, to allow processing programs for specific applications. Access to the processors is controlled, for example, via dispatch Priorities. These all work units of a service class have the same priority is assigned, but the assignment of these priority must not agree in every case with the definition of the importance of the service class. Rather, it is based on the current load of the system, the requirements of the class and its goal fulfillment. This behavior of the z / OS WLM is also called goal-oriented workload management, and it is an important distinguishing criterion to anteilsorientiertem workload management, will be awarded at the firm access to resources. The latter is often found in Workload Management components of Unix systems.
The second essential difference of the z / OS WLM to other workload management component is the strong integration with the applications and program products that run under z / OS operating system. So it is possible by constant communication between the WLM and these applications to detect and control the system through the WLM the transactions of the applications. This is so far on any other system possible where any control is limited to processes.
Besides the control of a system of z / OS WLM provides a set of interfaces that allow load balancing components to obtain information from the system to make an intelligent distribution of work on one or more z / OS systems. Multiple z / OS systems can be connected together in a Parallel Sysplex, and this combination is also supported to deliver a unified image to the outside. z / OS WLM also has a number of other functions that support the load distribution on a physical system between multiple logical systems and control access to large disk farms, depending on the daraufzugreifenden work.