System Management Guide:
Operating System and Devices

WLM Troubleshooting Guidelines

If you are not seeing the desired behavior with your current configuration, you might need to adjust your WLM configuration. The consumption values for each class can be monitored using tools such as wlmstat, wlmmon or wlmperf. This data can be collected and analyzed to help determine what changes might need to be made to the configuration. After you update the configuration, update the active WLM configuration using the wlmcntrl -u command.

The following guidelines can help you decide how to change your configuration:

• If the number of active shares in a tier varies greatly over time, you can give a class no shares for a resource so it can have a consumption target that is independent from the number of active shares. This technique is useful for important classes that require high-priority access to a resource.
• If you need to guarantee access to a certain amount of a resource, specify minimum limits. This technique is useful for interactive jobs that do not consume a lot of resources, but must respond quickly to external events.
• If you need to limit access to resources but shares do not provide enough control, specify maximum limits. In most cases, soft maximum limits are adequate, but hard maximums can be used for strict enforcement. Because hard maximum limits can result in wasted system resources, and they can increase paging activity when used for memory regulation, you should impose minimum limits for the other classes before imposing any hard limits.
• If less-important jobs are interfering with more-important jobs, put the less-important jobs in a lower tier. This technique ensures less-important jobs have lower priority and cannot compete for available resources while the more-important jobs are running.
• If a class cannot reach its consumption target for a resource, check whether this condition is caused by contention for another resource. If so, change the class allocation for the resource under contention.
• If processes within a class vary greatly in their behaviors or resource consumption, create more classes to gain more granular control. Also, it might be desirable to create a separate class for each important application.
• If your analysis shows the resource required by one class is dependent on the consumption of another class, reallocate your resources accordingly. For example, if the amount of resource required by ClassZ is dependent on the number of work requests that can be handled by ClassA, then ClassA must be guaranteed access to enough resources to provide what ClassZ needs.
• If one or more applications are consistently not receiving enough resources to perform adequately, your only option might be to reduce the workload on the system.