| 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 unique opportunities for database research. However, it is also important to understand the cost of virtualization. Virtual machine technologies add a layer of indirection between applications and the hardware that they use (e.g. CPU, memory, disk). This added complexity results in a performance overhead for software systems running in a virtual machine. In this thesis, we present an experimental study of the overhead of running a database workload in a virtual machine. Using a TPC-H workload running on PostgreSQL in a Xen virtual machine environment, we show that Xen does indeed introduce overhead for system calls, page fault handling, and disk I/O. However, these overheads do not translate to a high overhead in query execution time. We show that in all cases the average overhead is less than 10% and, therefore, conclude that the advantages of running a database system in a virtual machine do not come at a high cost in performance. |
