The effects of virtualization on main memory systems

Virtualization is mainly employed for increasing the utilization of a lightly-loaded system by consolidation, but also to ease the administration based on the possibility to rapidly provision or migrate virtual machines. These facilities are crucial for efficiently managing large data centers. At the same time, modern hardware --- such as Intel's Nehalem microarchitecure --- change critical assumptions about performance bottlenecks and software systems explicitly exploiting the underlying hardware --- such as main memory databases --- gain increasing momentum. In this paper, we address the question of how these specialized software systems perform in a virtualized environment. To do so, we present a set of experiments looking at several different variants of in-memory databases: The MonetDB Calibrator, a fine-grained hybrid row/column in-memory database running an OLTP workload, and an in-memory column store database running a multi-user OLAP workload. We examine how memory management in virtual machine monitors affects these three classes of applications. For the multi-user OLAP experiment we also experimentally compare a virtualized Nehalem server to one of its predecessors. We show that saturation of the memory bus is a major limiting factor but is much less impactful on the new architecture.