Be Aware of Your Leaders

TL;DR

This paper introduces Carousel, a reputation-based leader rotation framework for blockchain SMR systems that improves performance and fault tolerance by avoiding fixed leader schedules and utilizing on-chain information for leader selection.

Contribution

It proposes a novel Leader-Aware SMR framework with a formal leader-utilization requirement and introduces Carousel, a new adaptive leader-rotation mechanism that enhances throughput and resilience.

Findings

Over 2x throughput increase in faultless settings

20x throughput increase with faults

5x latency reduction with faults

Abstract

Advances in blockchains have influenced the State-Machine-Replication (SMR) world and many state-of-the-art blockchain-SMR solutions are based on two pillars: Chaining and Leader-rotation. A predetermined round-robin mechanism used for Leader-rotation, however, has an undesirable behavior: crashed parties become designated leaders infinitely often, slowing down overall system performance. In this paper, we provide a new Leader-Aware SMR framework that, among other desirable properties, formalizes a Leader-utilization requirement that bounds the number of rounds whose leaders are faulty in crash-only executions. We introduce Carousel, a novel, reputation-based Leader-rotation solution to achieve Leader-Aware SMR. The challenge in adaptive Leader-rotation is that it cannot rely on consensus to determine a leader, since consensus itself needs a leader. Carousel uses the available on-chain information to determine a leader locally and achieves Liveness despite this difficulty. A HotStuff implementation fitted with Carousel demonstrates drastic performance improvements: it increases throughput over 2x in faultless settings and provided a 20x throughput increase and 5x latency reduction in the presence of faults.