Book Image

MySQL 5.1 Plugin Development

Book Image

MySQL 5.1 Plugin Development

Overview of this book

MySQL has introduced a Plugin API with its latest version – a robust, powerful, and easy way of extending the server functionality with loadable modules on the fly. But until now anyone wishing to develop a plugin would almost certainly need to dig into the MySQL source code and search the Web for missing bits of the information.This is the first book on the MySQL Plugin API. Written together with one of the Plugin API primary architects, it contains all the details you need to build a plugin. It shows what a plugin should contain and how to compile, install, and package it. Every chapter illustrates the material with thoroughly explained source code examples.Starting from the basic features, common to all plugin types, and the structure of the plugin framework, this book will guide you through the different plugin types, from simple examples to advanced ones. Server monitoring, full-text search in JPEG comments, typo-tolerant searches, getting the list of all user variables, system usage statistics, or a complete storage engine with indexes – these and other plugins are developed in different chapters of this book, demonstrating the power and versatility of the MySQL Plugin API and explaining the intricate details of MySQL Plugin programming.
Table of Contents (16 chapters)
MySQL 5.1 Plugin Development
Credits
About the Authors
About the Reviewer
Preface

Writing UDFs


UDFs can be of two types, normal and aggregate. Normal UDFs take inputs and deliver an output just like an ordinary function in most programming languages. When run on a set of rows, they will return a result for every row. Aggregate UDFs take a group of rows, process each row, and produce a result at the end. In other words, they will return one result per group. Therefore, aggregate functions are useful for tasks such as adding up a group of values or calculating an average.

Whether MySQL considers a given UDF as an aggregate or a normal type depends on how it was installed. However, the API is somewhat different too, and we need to take care to install UDFs that use the aggregate API as aggregate and normal UDFs as normal. Otherwise they will not only fail to work correctly, but may as well crash the whole server.

Why write UDFs

There are several advantages and disadvantages to UDFs that we should be aware of. UDFs are much easier to develop than is hacking raw code into the...