10.2. Understanding Performance Tuning

Performance tuning is the process of improving the way a program operates. It involves taking a program and seeing what can be done to improve performance in an intelligent, controlled manner. As you might imagine, a tuned program is one that gets the most from the existing hardware and software environment.

Performance tuning involves measuring, evaluating, and modifying a program until it uses the minimum amount of computer resources to complete its execution. The biggest problem with the tuning process is that it is sometimes difficult to determine the amount of computer resources a program uses. Complicating matters further, adequate and complete information about resource utilization is often unavailable. In fact, no simple formula exists to determine how efficiently a program runs. Often the only way to assess whether a program is running efficiently is to evaluate its performance under varying conditions, such as during interactive use or during shortages of specific resources including memory and storage.

Performance issues may be difficult to identify. It is possible to have a program that operates without any apparent problem, but does not perform as efficiently as it could. In fact a program may perform well in one environment and poorly in another. Take for example an organization that has a shortage of Direct Access Storage Device (DASD). A program that uses excessive amounts of this resource may be deemed a poor performer under these circumstances. But if the same program were run in an environment that had adequate levels of DASD, it may not be suspected or tagged as a poor performer. This distinction demonstrates the subjectivity that is frequently used to determine how a program performs and how it is linked to the specific needs (related to resource issues) an organization has at any point in time.