SMR-X: Flexible Parallel State Machine Replication for Cloud Computing

Abstract

State Machine Replication (SMR) is a fundamental fault tolerant technique for distributed systems. SMR traditionally requires sequential execution of commands at each replica node, so as to guarantee strong consistency among replicas. To achieve high performance at large scale cloud datacenters, SMR has been parallelized by employing multiple threads at each replica. In this paper, we propose SMR-X, a novel parallel SMR scheme, which realizes flexible mapping of commands for parallel executing at each replica. The mapping between clients' requests and work threads is dynamically adjusted according to the load level of work threads. Therefore, workloads of different threads can be well balanced and high system throughput can be achieved. The major challenge in our work lies in the inconsistency problem caused by dynamic changes in request-thread mapping. To cope with this, we design delicate mechanisms to synchronize mapping function, so that strong consistency among replicas can be guaranteed. The correctness of the proposed scheme is rigorously proved and its performance is evaluated via simulations. Simulation results show that SMR-X can achieve better load balance and lower access latency than existing parallel SMR schemes.