Boosting State Machine Replication with Concurrent Execution

Abstract

State machine replication is a fundamental technique to render services fault tolerant. One of the key assumptions of state machine replication is that replicas must execute operations deterministically. Deterministic execution often translates into sequential execution of requests at replicas. With the increasing demand for dependable services and widespread use of multi-core servers, several proposals for enabling concurrent execution in state machine replication have appeared in the literature. Invariably, these techniques exploit the fact that independent operations, those that do not share any common state or do not update shared state, can execute concurrently. Existing protocols differ in several important ways. In this paper, we survey this field of research and discuss the main aspects of the different protocols. Central aspects include conflict detection, representation and enforcing; tradeoffs involving existing architectures and level of allowed parallelism; workload-driven adaptation schemes; and implications of parallel state machine replication to recovery. Moreover, we discuss ongoing and future work directions for high-throughput state machine replication.