Web Performance Tuning, 2nd Edition

Chapter 4. Performance Monitoring

The first thing you should do in tuning a web site is to monitor that site so you can see patterns and trends. From this you’ll know whether you’re helping or not. And as we will see later, the same programs we write for monitoring can also be used for load testing.

In this chapter, we first define some parameters of performance. Then we show how to monitor them with free software from http://patrick.net/, without installing anything on production machines.

Parameters of Performance

There are four classic parameters describing the performance of any computer system: latency, throughput, utilization, and efficiency. Tuning a system for performance can be defined as minimizing latency and maximizing the other three parameters. Though the definition is straightforward, the task of tuning itself is not, because the parameters can be traded off against one another and will vary with the time of day, the sort of content served, and many other circumstances. In addition, some performance parameters are more important to an organization’s goals than others.

Latency and Throughput

Latency is the time between making a request and beginning to see a result. Some define latency as the time between making a request and the completion of the response, but this definition does not clearly distinguish the psychologically significant time spent waiting, not knowing whether a request has been accepted or understood. You will also see latency defined as the inverse ...