Section 16.1. Performance Fundamentals

16.1. Performance Fundamentals

When you start designing, building, and tuning your database system, you need to try to balance the three main areas that affect your performance:

• CPU usage

• I/O utilization

• Memory usage

At least one of these three areas is affected by any change that you make, either in designing the system or tuning the system using the registry variables or DB2 configuration parameters. For example, increasing the size of one or more of your buffer pools will increase the memory consumption on the server, but it may then decrease the I/O that is required. By understanding how the various registry variables and configuration parameters impact the CPU usage, I/O, and memory usage, you will be better prepared to judge whether the changes will help the performance of the system.

Let's take another example. If you have a system that is already paging (or swapping) but is not doing a lot of I/O operations, increasing the size of the buffer pools will not be a good idea since this will further increase the paging operations but will not likely reduce the I/O much less than the current level. This change might actually reduce the overall performance of the system, so by thinking this through you can save time and effort in the tuning process.