What WLM does
One z/OS system runs online transactions, batch, databases and system tasks at the same time. Workload Manager decides moment by moment who gets the resources, based on goals the installation writes in business terms.
Goals, not priorities
Older systems made operators set dispatching priorities by hand. z/OS instead runs in goal mode: the installation says what each kind of work should achieve, such as 'card authorisations finish in under a quarter of a second', and WLM adjusts dispatching priority, storage and I/O priority to meet those goals.
The building blocks
| Term | What it is |
|---|---|
| Service definition | The whole WLM configuration for a sysplex, stored in the WLM couple dataset |
| Service policy | A named set of goals that can be activated, for example a weekday and a month-end policy |
| Workload | A group of service classes for reporting, such as ONLINE or BATCH |
| Service class | A group of work with the same goal and importance |
| Period | A stage within a service class; work can move to a later period with an easier goal as it uses more resources |
| Classification rules | Rules that assign incoming work to a service class |
| Report class | An extra grouping used only for reporting, so you can measure work without changing how it is managed |
Importance
Each goal has an importance from 1 (most important) to 5. When there is not enough capacity for everything, WLM helps the most important work that is missing its goal first, taking resources from less important work. Work with a discretionary goal gets whatever is left over.
Common mistakes
WLM does not decide when batch jobs start (the workload scheduler does). It manages resources for work that is already running, and can manage batch initiators.
If every class is most important, none is. Importance only works when it reflects real business priorities.
Policy changes affect the whole sysplex. They go through change control and capacity review.
What you will see at work
- System programmers and performance analysts own the service definition; application teams request service classes for new workloads.
- Production support sees WLM's effects every day: slow online response or late batch is often a classification or capacity question.
- Many sites have separate policies for normal days and peaks such as month end.
Key terms
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