MySQL Troubleshooting

Preface

I have worked since May 2006 as a principal technical support engineer in the Bugs Verification Group of the MySQL Support Group for MySQL AB, then Sun, and finally Oracle. During my daily job, I often see users who are stuck with a problem and have no idea what to do next. Well-verified methods exist to find the cause of the problem and fix it effectively, but they are hard to cull from the numerous information sources. Hundreds of great books, blog posts, and web pages describe different parts of the MySQL server in detail. But here’s where I see the difficulty: this information is organized in such a way as to explain how the MySQL server normally works, leaving out methods that can identify failures and ill-posed behavior.

When combined, these information sources explain each and every aspect of MySQL operation. But if you don’t know why your problem is occurring, you’ll probably miss the cause among dozens of possibilities suggested by the documentation. Even if you ask an expert what could be causing your problem, she can enumerate many suspects, but you still need to find the right one. Otherwise, any changes you make could just mask the real problem temporarily, or even make it worse.

It is very important to know the source of a problem, even when a change to an SQL statement or configuration option can make it go away. Knowledge of the cause or failure will arm you to overcome it permanently and prevent it from popping up again in the future.

I wrote this book to give you the methods I use constantly to identify what caused an error in an SQL application or a MySQL configuration and how to fix it.

Audience

This book is written for people who have some knowledge about MySQL. I tried to include information useful for both beginners and advanced users. You need to know SQL and have some idea of how the MySQL server works, at least from a user manual or beginner’s guide. It’s better yet if you have real experience with the server or have already encountered problems that were hard to solve.

I don’t want to repeat what is in other information sources; rather, I want to fill those gaps that I explained at the beginning of this Preface. So you’ll find guidance in this book for fixing an application, but not the details of application and server behavior. For details, consult the MySQL Reference Manual (http://dev.mysql.com/doc/refman/5.5/en/index.html).