Since Grails is built on Java technology to set-up a data source requires some knowledge of JDBC (the technology that doesn't stand for Java Database Connectivity).

Essentially, if you are using another database other than HSQLDB you need to have a JDBC driver. For example for MySQL you would need Connector/J

Drivers typically come in the form of a JAR archive. Drop the JAR into your projects lib directory.

Once you have the JAR in place you need to get familiar Grails' DataSource descriptor file located at grails-app/conf/DataSource.groovy. This file contains the dataSource definition which includes the following settings:

A typical configuration for MySQL may be something like:

dataSource {
	pooled = true
	dbCreate = "update"
	url = "jdbc:mysql://localhost/yourDB"
	driverClassName = "com.mysql.jdbc.Driver"
	username = "yourUser"
	password = "yourPassword"	
}

When configuring the DataSource do not include the type or the def keyword before any of the configuration settings as Groovy will treat these as local variable definitions and they will not be processed. For example the following is invalid:

dataSource {
	boolean pooled = true // type declaration results in local variable
	…
}

Example of advanced configuration using extra properties:

dataSource {
	pooled = true
	dbCreate = "update"
	url = "jdbc:mysql://localhost/yourDB"
	driverClassName = "com.mysql.jdbc.Driver"
	username = "yourUser"
	password = "yourPassword"
	properties {
		maxActive = 50
		maxIdle = 25
		minIdle = 5
		initialSize = 5
		minEvictableIdleTimeMillis = 60000
		timeBetweenEvictionRunsMillis = 60000
		maxWait = 10000		
	}	
}