Preface

These days, it seems that most discussion of open-source software centers on the idea that you should not have to tie your future to the whim of some giant corporation. People say that open -source software is better than proprietary software because it is developed and maintained by the users instead of a faceless company out to lighten your wallet.

I think that the real value in free software is education. I have never learned anything by reading my own code ^[1] . On the other hand, it's a rare occasion when I've looked at code written by someone else and haven't come away with another tool in my toolkit. People don't think alike. I don't mean that people disagree with each other; I mean that people solve problems in different ways. Each person brings a unique set of experiences to the table. Each person has his own set of goals and biases. Each person has his own interests. All these things will shape the way you think about a problem. Often, I'll find myself in a heated disagreement with a colleague only to realize that we are each correct in our approach. Just because I'm right, doesn't mean that my colleague can't be right as well.

^[1] Maybe I should say that I have never learned anything new by reading my own code. I've certainly looked at code that I've written and wondered what I was thinking at the time, learning that I'm not nearly as clever as I had remembered . Oddly enough, those who have read my code have reached a similar conclusion.

Open-source software is a great way to learn. You can learn about programming. You can learn about design. You can learn about debugging. Sometimes, you'll learn how not to design, code, or debug; but that's a valuable lesson too. You can learn small things, such as how to cache file descriptors on systems where file descriptors are a scarce and expensive resource, or how to use the select() function to implement fine-grained timers. You can learn big things, like how a query optimizer works or how to write a parser, or how to develop a good memory management strategy.

PostgreSQL is a great example. I've been using databases for the last two decades. I've used most of the major commercial databases: Oracle, Sybase, DB2, and MS SQL Server. With each commercial database, there is a wall of knowledge between my needs and the vendor's need to protect his intellectual property. Until I started exploring open-source databases, I had an incomplete understanding of how a database works. Why was this particular feature implemented that way? Why am I getting poor performance when I try this? That's a neat feature; I wonder how they did that? Every commercial database tries to expose a small piece of its inner workings. The explain statement will show you why the database makes its optimization decisions. But, you only get to see what the vendor wants you to see. The vendor isn't trying to hide things from you (in most cases), but without complete access to the source code, they have to pick and choose how to expose information in a meaningful way. With open source software, you can dive deep into the source code and pull out all the information you need. While writing this book, I've spent a lot of time reading through the PostgreSQL source code. I've added a lot of my own code to reveal more information so that I could explain things more clearly. I can't do that with a commercial database.

There are gems of brilliance in most open-source projects. In a well-designed, well- factored project, you will find designs and code that you can use in your own projects. Many open source projects are starting to split their code into reusable libraries. The Apache Portable Runtime is a good example. The Apache Web server runs on many diverse platforms. The Apache development team saw the need for a layer of abstraction that would provide a portable interface to system functions such as shared memory and network access. They decided to factor the portability layer into a library separate from their main project. The result is the Apache Portable Runtime - a library of code that can be used in other open-source projects (such as PostgreSQL).

Some developers hate to work on someone else's code. I love working on code written by another developer “ ”I always learn something from the experience. I strongly encourage you to dive into the PostgreSQL source code. You will learn from it. You might even decide to contribute to the project.