Pachev - Understanding MySQL Internals

This book can be useful for a number of readers: a developer trying to extend MySQL in some way; a DBA or database application programmer interested in how exactly MySQL runs his queries; a computer science student learning about database kernel development; a developer looking for ideas while working on a product that requires extensive database functionality that he must implement himself; a closed-source database developer wondering how in the world MySQL runs its queries so fast; a random, curious computer geek who has used MySQL some and wonders what is inside; and, of course, anybody who wants to look smart by having a book on MySQL internals displayed on his shelf.

Although MySQL source is open in the sense of being publicly available, it is in essence closed to you if you do not understand it. It may be intimidating to look at several hundred thousand lines of code written by gifted programmers that elegantly and efficiently solves difficult problems one line at a time. To understand the code, you will need a measure of the inspiration and perspiration of those who created it. Hopefully, this book can provide enough guidance to remove those barriers and to open the source of MySQL for you.

I do not believe it is possible to understand and appreciate MySQL strictly through a conceptual discussion. On a high conceptual level MySQL is very simple. It does not implement many revolutionary ideas. It sticks to the basics. Why is it so popular then? Why do we know enough about it for O'Reilly to be willing to publish a book on its internals?

The reason, in my opinion, is that what makes a good database is not so much the concepts behind it, but how well they are implemented. It is important to be conceptually sound on a basic level, but a good portion of the genius is in implementing those concepts in a way that provides a reasonable combination of good performance and the ease of maintenance. In other words, the devil is in the details, and MySQL developers have done a great job of taking that devil by the horns and twisting his head off.

Thus, in order to appreciate the inner workings of MySQL, you need to get close to the places where that devil is being subdued. Somewhere in the dark depths of the optimizer or inside the B-tree, there is music to be heard as you study the code. It will take some work to hear that music, but once you do, you can feel its beauty. And to hear the music you must not be afraid to compile the code, add a few debugging messages to help you understand the flow, and perhaps even change a few things to appreciate what will make the server crash (and how) if you fail to handle something that turns out to be important after all.