When the Virtual Machine Wins over the Container: DBMS Performance and Isolation in Virtualized Environments

Database management systems (DBMSs) are a common service in the cloud. Cloud providers employ virtualization to consolidate DBMSs for efficient resource utilization and to isolate collocated DBMS workloads. To guarantee the service-level agreement (SLA), the disk I/O performance and its isolation are critical in DBMSs because they are inherently disk I/O intensive. This paper investigates the disk I/O performance and its isolation of MySQL on two major virtualization platforms, KVM and LXC. KVM provides the hypervisor-based virtualization (virtual machines) while LXC provides the operating-system-level virtualization (containers). Containers are widely believed to outperform virtual machines because of negligible virtualization overheads, while virtual machines are to provide stronger performance isolation. Contrary to the general belief, our results show that KVM outperforms LXC by up to 95% in MySQL throughput without compromising the isolation. Furthermore, LXC violates the performance isolation; a container given 30% share of the disk bandwidth consumes the 70% share. Our analysis reveals that the file system journaling, which is mandatory to maintain file system consistency, has negative impact on both the performance and its isolation in the container. Because of the sharing of the journaling module in containers, the journaling activities are serialized and bundled with each other, resulting in poor performance and violation of the performance isolation.