18.3 Identifying Performance Objectives

Objectives are the most important input to the performance-management process. Before you can begin to address or even identify a problem, you must understand exactly what level of performance is considered acceptable. Reasonable objectives should be developed by consulting with users and management. These objectives guide your performance-management activities and assist you in reconciling performance trade-offs between one application and another.

Performance objectives should indicate how quickly the system should process and respond to particular user requests or activities. This can be difficult to specify for applications that involve many different functions, but you do not necessarily have to establish and track response times for every activity. To approximate overall response time, focus on key activities or on activities that seem to be representative of overall use. For example, for a word-processing application, you might want to measure the time required to invoke the application, or the time to perform a spell-check on an average-sized document. On the other hand, for a batch job that performs a database update, you might want to measure only the total elapsed time it takes to perform the update.

Application objectives should also include an estimated number of concurrent uses. By documenting this estimate, you will be better prepared to explain and deal with deteriorating performance when the number of users accessing an application mysteriously increases from 30 to 60. Finally, no OpenVMS system can produce a particular response time 100 percent of the time, because of unpredictable...