The WebSphere XD has a concept of service policy that lets you define performance goals for application or actually application URL and decide the priority of application compaired to other applications.
Once an administrator has classified an application's URLs and connected them to service policies, then the ODR will begin examining incoming URLs and compare their performance characteristics to the goals defined in the corresponding service policies. The ODR can accomplish this through several mechanisms:
- The ODR can use its knowledge of the relative priorities of different service policies to determine how long requests will wait in its own internal queues; higher-priority requests will receive service before lower-priority requests when resources are constrained.
- The ODR can use its knowledge of response time goals and the relative availability of resources (CPU and memory) in different cluster members to perform dynamic workload management.
- The ODR can work with other parts of the system to achieve dynamic placement within a dynamic cluster. Dynamic placement is a facility in which the XD autonomic managers determine how many copies of an application server are appropriate within a cluster. For example, if one application is performing well above its performance goals, while another higher- or equal-priority application is underperforming because the machines running clustered copies of that application are overtaxed, then the autonomic manager can decide to adjust the number of application servers running each application, decreasing the former and increasing the latter to improve the performance of the overwhelmed application.
Some of these facilities (such as the classification and queuing of work) are entirely the function of the ODR, and will work well with many different types of workloads. Others (such as dynamic placement) are more specialized and work in concert with other parts of the XD system. All require require the use of the ODR, which is the fundamental architectural linchpin of XD, and possesses still more features.