Foundations of Scalable Systems

Chapter 1. Introduction to Scalable Systems

The last 20 years have seen unprecedented growth in the size, complexity, and capacity of software systems. This rate of growth is hardly likely to slow in the next 20 years—what future systems will look like is close to unimaginable right now. However, one thing we can guarantee is that more and more software systems will need to be built with constant growth—more requests, more data, and more analysis—as a primary design driver.

Scalable is the term used in software engineering to describe software systems that can accommodate growth. In this chapter I’ll explore what precisely is meant by the ability to scale, known (not surprisingly) as scalability. I’ll also describe a few examples that put hard numbers on the capabilities and characteristics of contemporary applications and give a brief history of the origins of the massive systems we routinely build today. Finally, I’ll describe two general principles for achieving scalability, replication and optimization, which will recur in various forms throughout the rest of this book, and examine the indelible link between scalability and other software architecture quality attributes.

What Is Scalability?

Intuitively, scalability is a pretty straightforward concept. If we ask Wikipedia for a definition, it tells us, “Scalability is the property of a system to handle a growing amount of work by adding resources to the system.” We all know how we scale a highway system—we add more traffic ...