Chapter 1. An Introduction to Performance Tuning
Going faster seems to be a central part of human development. As little as three hundred years ago, the fastest you could expect to go was a few tens of miles an hour, aboard a fast clipper ship with a stiff wind behind you. Now, we must expand our view to things such as the fastest achievable speed while remaining in the Earth's atmosphere -- perhaps fifteen hundred miles an hour , twice the speed of sound, if you are a civilian without access to the latest, fastest military aircraft. The journey that used to take three weeks under sail from London to New York City now takes us as little as two and a half hours, sipping champagne the whole way. This innate human desire to go fast is expressed in many ways: microwave ovens let us cook dinner quickly, high-performance automobiles and motorcycles give us a wonderful thrill, email lets us communicate at almost the speed of thought. But what happens when that email server is overwhelmed, as when we all log in at eight o'clock in the morning to check what has gone on while we've slept? Or when the procurement system for the company that distributes microwave ovens is only able to handle half of the workload, or when a mechanical engineer's CAD system runs so slowly that the car engine she's designing won't be ready in time for the new model year? These are the problems facing us in performance tuning: it is the adaptation of the speed of a computer system to the speed requirements imposed by the real world. Sometimes these problems are subtle, sometimes not. We must carefully consider the changes in the system that caused it to become unacceptably slow. These influences might come from within, such as a heavier load placed on the system, or from without, such as a new operating system revision subtly changing -- or utterly replacing -- an algorithm for resource management that is critically important to our software. The solutions are sometimes quick (a matter of adjusting one "knob" slightly), or sometimes slow and painful (a task for weeks of analysis, consultations with vendors , and careful redesign of an infrastructure). When I originally started work on this book, it seemed straightforward: take Mike Loukides's excellent but dated first edition and overhaul it for modern computer systems. As I progressed further along, I realized that this book is actually about much more than simply performance tuning. It really covers two distinct areas:
These areas are all underpinned by the science of computer architecture. This book does not concentrate on application design; rather, it focuses on the operating system, the underlying hardware, and their interactions. To most systems administrators, a computer is really a black box. This is perfectly reasonable for many tasks : after all, it's certainly not necessary to understand how the operating system manages free memory to configure and maintain a mail server. However, in performance tuning -- which is, at heart, very much about the underlying hardware and how it is abstracted -- truly understanding the behavior of the system involves a detailed knowledge of the inner workings of the machine. In this chapter, we'll briefly discuss some of the most important concepts of computer architecture, and then go into the fundamental principles of performance tuning. |
