RotorcRaft: Scalable Follower-Driven Raft on RDMA

State machine replication plays a fundamental role in meeting both the scalability and the fault-tolerance requirement in cloud services. However, the single-point leader is easy to become a bottleneck of scalability because it needs to handle all read and write requests and independently replicate logs in order for all followers. Moreover, machine resources are shared through cloud services where the scale-up of the leader is very expensive. In this paper, we propose a variant of Raft protocol using RDMA named RotorcRaft to significantly offload burden from the leader to followers to relieve the single-point bottleneck. First, RotorcRaft assigns a follower-driven log replication mechanism that exploits hybrid RDMA primitives to relieve part of the burden of leader to followers in log replication. Then, RotorcRaft proposes a quorum follower read that enables followers to handle read requests without the involvement of the leader. Experimental results demonstrate that RotorcRaft has excellent scalability and up to 1.4x higher throughput with 84% latency compared against the state-of-the-art work.