We assume you are reading this book because you want to know more about Hadoop at a hands-on level; the key audience is those with software development experience but no prior exposure to Hadoop or similar big data technologies.

For developers who want to know how to write MapReduce applications, we assume you are comfortable writing Java programs and are familiar with the Unix command-line interface. We will also show you a few programs in Ruby, but these are usually only to demonstrate language independence, and you don't need to be a Ruby expert.

For architects and system administrators, the book also provides significant value in explaining how Hadoop works, its place in the broader architecture, and how it can be managed operationally. Some of the more involved techniques in Chapter 4, Developing MapReduce Programs, and Chapter 5, Advanced MapReduce Techniques, are probably of less direct interest to this audience.