1. A computer-implemented method of analyzing the performance of a server, the method comprising: monitoring a first performance metric of the server over a period of time to generate a series of values of the first performance metric, wherein the server system responds to requests from clients during said period of time; monitoring a second performance metric of the server system over said period of time to generate a series of values of the second performance metric; and measuring a degree to which the first performance metric and the second performance metric are related at least in-part by calculating a correlation coefficient between the series of values of the first performance metric and the series of values of the second performance metric.