Remora: A Low-Latency DAG-Based BFT Through Optimistic Paths

Standing as a foundational element within blockchain systems, the Byzantine Fault Tolerant (BFT) consensus has garnered significant attention over the past decade. The introduction of a Directed Acyclic Directed (DAG) structure into BFT consensus design, termed DAG-based BFT, has emerged to bolster throughput. However, prevalent DAG-based protocols grapple with substantial latency issues, suffering from a latency gap compared to non-DAG protocols. For instance, leading-edge DAG-based protocols named GradedDAG and BullShark exhibit a good-case latency of $4$ and $6$ communication rounds, respectively. In contrast, the non-DAG protocol, exemplified by PBFT, attains a latency of $3$ rounds in favorable conditions. To bridge this latency gap, we propose Remora, a novel DAG-based BFT protocol. Remora achieves a reduced latency of $3$ rounds by incorporating optimistic paths. At its core, Remora endeavors to commit blocks through the optimistic path initially, facilitating low latency in favorable situations. Conversely, in unfavorable scenarios, Remora seamlessly transitions to a pessimistic path to ensure liveness. Various experiments validate Remora's feasibility and efficiency, highlighting its potential as a robust solution in the realm of BFT consensus protocols.