The following guidelines should help you develop an overall approach to performance tuning.
Remember the Law of Diminishing Returns: Your greatest performance benefits usually come from your initial efforts. Further changes generally produce smaller and smaller benefits and require more and more effort.
Do Not Tune Just for the Sake of Tuning: Tune to relieve identified constraints. If you tune resources that are not the primary cause of performance problems, this has little or no effect on response time until you have relieved the major constraints, and it can actually make subsequent tuning work more difficult. If there is any significant improvement potential, it lies in improving the performance of the resources that are major factors in the response time.
Consider the Whole System: You can never tune one parameter or system in isolation. Before you make any adjustments, consider how it will affect the system as a whole.
Change One Parameter at a Time: Do not change more than one performance tuning parameter at a time. Even if you are sure that all the changes will be beneficial, you will have no way of evaluating how much each change contributed. You also cannot effectively judge the trade-off you have made by changing more than one parameter at a time. Every time you adjust a parameter to improve one area, you almost always affect at least one other area that you may not have considered.
Measure and Reconfigure by Levels: For the same reasons that you should only change one parameter at a time, tune one level of your system at a time. You can use the following list of levels within a system as a guide:
Check for Hardware and Software Problems: Some performance problems may be corrected by applying service either to your hardware, or to your software, or to both. Do not spend excessive time monitoring and tuning your system when simply applying service may make it unnecessary.
Understand the Problem Before You Upgrade Your Hardware: Even if it seems that additional storage or processor power could immediately improve performance, take the time to understand where your bottlenecks are. You may spend money on additional disk storage only to find that you do not have the processing power or the channels to exploit it.
Put Fallback Procedures in Place Before You Start Tuning: As noted earlier, some tuning can cause unexpected performance results. If this leads to poorer performance, it should be reversed and alternative tuning tried. If the former setup is saved in such a manner that it can be simply recalled, the backing out of the incorrect information becomes much simpler.