Blockchain technology sparked renewed interest in planetary-scale Byzantine fault-tolerant (BFT) state machine replication (SMR). While recent works predominantly focused on improving the scalability and throughput of these protocols, few of them addressed latency. We present Mercury, a novel transformation to autonomously optimize the latency of quorum-based BFT consensus. Mercury employs a dual resilience threshold that enables faster transaction ordering when the system contains few faulty replicas. Mercury allows forming compact quorums that substantially accelerate consensus using a smaller resilience threshold. Nevertheless, Mercury upholds standard SMR safety and liveness guarantees with optimal resilience, thanks to its judicious use of a dual operation mode and BFT forensics techniques. Our experiments spread tens of replicas across continents and reveal that Mercury can order transactions with finality in less than 0.4 seconds, half the time of a PBFT-like protocol (optimal in terms of number of communication steps and resilience) in the same network. Furthermore, Mercury matches the latency of running its base protocol on theoretically optimal internet links (transmitting at 67% of the speed of light).

翻译：区块链技术重新激发了人们对行星级拜占庭容错（BFT）状态机复制（SMR）的兴趣。虽然近期研究主要集中于提升此类协议的可扩展性与吞吐量，但鲜有工作关注延迟问题。本文提出 Mercury，一种新颖的转换机制，旨在自主优化基于法定人数的 BFT 共识延迟。Mercury 采用双重弹性阈值，使得当系统中存在少量故障副本时能够实现更快的交易排序。通过使用更小的弹性阈值，Mercury 允许形成紧凑的法定人数，从而显著加速共识过程。尽管如此，凭借其对双重操作模式和 BFT 取证技术的审慎运用，Mercury 仍能以最优弹性维持标准的 SMR 安全性与活性保证。我们在各大洲部署数十个副本进行实验，结果表明 Mercury 能够在 0.4 秒内完成具有最终性的交易排序，这比相同网络环境下类 PBFT 协议（在通信步数与弹性方面最优）的耗时减少一半。此外，Mercury 的延迟表现与其基础协议在理论最优互联网链路（以光速的 67% 传输）上运行的延迟相当。