Article ID: 2025PAP0004
State Machine Replication (SMR) is a fundamental technique for building fault-tolerant distributed systems with strong consistency. Rabia is an SMR protocol that simplifies implementation design through a randomized consensus algorithm. Our analysis reveals a design limitation of the Rabia protocol: under partial network partitioning, replicas can develop inconsistent queue states, leading to a livelock state. We present Qsync, which enhances Rabia's fault tolerance through queue state synchronization mechanisms while preserving its implementation simplicity. Experimental evaluation shows that Qsync maintains stable performance under partial network partitions where the original Rabia throughput drops to zero.
