Moonshot: Optimizing Chain-Based Rotating Leader BFT via Optimistic Proposals

TL;DR

Moonshot targets the gap in chain-based rotating-leader BFT SMR by achieving a proposal delay of $δ$ between consecutive honest leaders and a constant commit latency of $3δ$ in the partially synchronous model. It introduces Simple Moonshot, Pipelined Moonshot, and Commit Moonshot—two pipelined variants with optimistic responsiveness and a non-pipelined variant—each designed to maintain reorg resilience and bounded view lengths while avoiding vulnerable vote-aggregator bottlenecks. Through WAN experiments against Jolteon, Moonshot demonstrates higher throughput and lower latency in failure-free and failure scenarios, while revealing that aggressive linearization strategies (e.g., vote-pipelining) can hurt practical performance in many settings. The work highlights a nuanced trade-off between communication complexity and real-world performance, showing that modestly higher messaging costs can yield substantial latency reductions and resilience benefits for large-scale, globally distributed deployments.

Abstract

Existing chain-based rotating-leader BFT SMR protocols for the partially synchronous network model with constant commit latencies incur block periods of at least $2δ$ (where $δ$ is the message transmission latency). While a protocol with a block period of $δ$ exists under the synchronous model, its commit latency is linear in the size of the system. To close this gap, we present the first chain-based BFT SMR protocols with $δ$ delay between the proposals of consecutive honest leaders and commit latencies of $3δ$. We present three protocols for the partially synchronous model under different notions of optimistic responsiveness, two of which implement pipelining. All of our protocols achieve reorg resilience and two have short view lengths; properties that many existing chain-based BFT SMR protocols lack. We present an evaluation of our protocols in a wide-area network wherein they demonstrate significant increases in throughput and reductions in latency compared to the state-of-the-art, Jolteon. Our results also demonstrate that techniques commonly employed to reduce communication complexity$\unicode{x2014}$such as vote-pipelining and the use of designated vote-aggregators$\unicode{x2014}$actually reduce practical performance in many settings.

Figures (10)

• Figure 1: The Simple Moonshot Protocol
• Figure 2: Optimistic proposal (pictured in blue) and vote multicasting (pictured in orange) enable Simple Moonshot and Pipelined Moonshot to propose new blocks at the same rate that they become certified when proposals and votes take equal time to propagate and process.
• Figure 3: The Pipelined Moonshot Protocol
• Figure 4: Commit Moonshot
• Figure 5: Explicit commit votes (pictured in green) enable Commit Moonshot to commit blocks sooner than its pipelined counterparts when block proposals (pictured in blue) take sufficiently longer to disseminate than votes.

Theorems & Definitions (76)

• Definition 1: Byzantine Fault-Tolerant State Machine Replication abraham2020sync
• Definition 2: Minimum View Change Block Period ($\omega$)
• Definition 3: Minimum Commit Latency ($\lambda$)
• Definition 4: View Length ($\tau$)
• Definition 5: Reorg Resilience
• Definition 6: Optimistic Responsiveness yin2019hotstuff
• Definition 7: Optimistic Responsiveness (Consecutive Honest) abraham2022optimal
• Claim 1: Quorum Intersection
• proof
• Claim 2: Honest Majority Intersection