Replication is essential for fault-tolerance. However, in in-memory systems, it is a source of high overhead. Remote direct memory access (RDMA) is attractive to create redundant copies of data, since it is low-latency and has no CPU overhead at the target. However, existing approaches still result in redundant data copying and active receivers. To ensure atomic data transfers, receivers check and apply only fully received messages. Tailwind is a zero-copy recovery-log replication protocol for scale-out in-memory databases. Tailwind is the first replication protocol that eliminates all CPU-driven data copying and fully bypasses target server CPUs, thus leaving backups idle. Tailwind ensures all writes are atomic by leveraging a protocol that detects incomplete RDMA transfers. Tailwind substantially improves replication throughput and response latency compared with conventional RPC-based replication. In symmetric systems where servers both serve requests and act as replicas, Tailwind also improves normal-case throughput by freeing server CPU resources for request processing. We implemented and evaluated Tailwind on RAMCloud, a low-latency in-memory storage system. Experiments show Tailwind improves RAMCloud’s normal-case request processing throughput by 1.7×. It also cuts down writes median and 99th percentile latencies by 2x and 3x respectively.

This work has been supported by the BigStorage project, funded by the European Union under the Marie SklodowskaCurie Actions (H2020-MSCA-ITN-2014-642963), by the Spanish Ministry of Science and Innovation (contract TIN2015- 65316), by Generalitat de Catalunya (contract 2014- SGR-1051). This material is based upon work supported by the National Science Foundation under Grant Nos. CNS-1566175 and CNS-1750558. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. This work was supported in part by Facebook and VMware.

Peer Reviewed