Database performance and query optimization
The goal of database performance tuning is to minimize the response time of your queries by making the best use of your system resources. The best use of these resources involves minimizing network traffic, disk I/O, and CPU time. This goal can only be achieved by understanding the logical and physical structure of your data, the applications used on your system, and how the conflicting uses of your database might affect performance.
The best way to avoid performance problems is to ensure that performance issues are part of your ongoing development activities. Many of the most significant performance improvements are realized through careful design at the beginning of the database development cycle. To most effectively optimize performance, you must identify the areas that yield the largest performance increases over the widest variety of situations. Focus your analysis on these areas.
Many of the examples within this publication illustrate a query written through either an SQL or an OPNQRYF query interface. The interface chosen for a particular example does not indicate an operation exclusive to that query interface, unless explicitly noted. It is only an illustration of one possible query interface. Most examples can be easily rewritten into whatever query interface that you prefer.