Virtual machine technologies offer simple and practical mechanisms to address many manageability problems in database systems. For example, these technologies allow for server consolidation, easier deployment, and more flexible provisioning. Therefore, database systems are increasingly being run on virtual machines. This offers many opportunities for researchers in self-managing database systems, but it is also important to understand the cost of virtualisation. In this paper, we present an experimental study of the overhead of running a database workload on a virtual machine. We show that the average overhead is less than 10%, and we present details of the different causes of this overhead. Our study shows that the manageability benefits of virtualisation come at an acceptable cost.