The Observation and Evaluation and Modification Phases are cyclical. After a baseline result has been recorded, some parameter or environmental settings might be changed to improve performance. The results of the change will be recorded and the cycle starts again. When changing any parameter or environmental setting, one item should be changed at a time, its affects observed and the item should keep changing until no improvement is gained.
A parameter change would be characterized as the modification of an application level setting e.g. making an application controlled cache or pool larger or smaller. An environmental change would be characterized as the modification of application�s runtime environment e.g. adding/subtracting memory or adding/subtracting CPUs.