The performance of a computer system is based on human expectations and the ability of the computer system to fulfill these expectations. The objective for performance tuning is to make those expectations and their fulfillment match. The path to achieving this objective is a balance between appropriate expectations and optimizing the available system resources. The performance-tuning process demands great skill, knowledge, and experience, and cannot be performed by only analyzing statistics, graphs, and figures. If results are to be achieved, the human aspect of perceived performance must not be neglected. Performance tuning must also usually take into consideration problem-determination aspects as well as pure performance issues.
Expectations can often be classified as either of the following:
| Throughput expectations | A measure of the amount of work performed over a period of time |
| Response time expectations | The elapsed time between when a request is submitted and when the response from that request is returned |
The performance-tuning process can be initiated for a number of reasons:
Performance tuning on a newly installed system usually involves setting some base parameters for the operating system and applications. The sections in this chapter describe the characteristics of different system resources and provide guidelines regarding their base tuning parameters, if applicable.
Limitations originating from the sizing phase will either limit the possibility of tuning, or incur greater cost to overcome them. The system may not meet the original performance expectations because of unrealistic expectations, physical problems in the computer environment, or human error in the design or implementation of the system. In the worst case, adding or replacing hardware might be necessary. Be particularly careful when sizing a system to allow enough capacity for unexpected system loads. In other words, do not design the system to be 100 percent busy from the start of the project.
When a system in a productive environment still meets the performance expectations for which it was initially designed, but the demands and needs of the utilizing organization have outgrown the system's basic capacity, performance tuning is performed to delay or even to avoid the cost of adding or replacing hardware.
Many performance-related issues can be traced back to operations performed by a person with limited experience and knowledge who unintentionally restricted some vital logical or physical resource of the system.