The Energy Efficiency of Database Replication Protocols

Replication is a widely used technique to provide high-availability to online services. While being an effective way to mask failures, replication comes at a price: at least twice as much hardware and energy are required to mask a single failure. In a context where the electricity drawn by data centers worldwide is increasing each year, there is a need to maximize the amount of useful work done per Joule, a metric denoted as energy efficiency. In this paper, we review commonly-used database replication protocols and experimentally measure their energy efficiency. We observe that the most efficient replication protocol achieves less than 60% of the energy efficiency of a stand-alone server on the TPC-C benchmark. We identify algorithmic techniques that can be used by any protocol to improve its efficiency. Some approaches improve performance, others lower power consumption. Of particular interest is a technique derived from primary-backup replication that implements a transaction log on low-power backups. We demonstrate how this approach can lead to an energy efficiency that is 79% of the one of a stand-alone server. This constitutes an important step towards reconciling replication with energy efficiency.