Shoal++: High Throughput DAG BFT Can Be Fast!

TL;DR

Shoal++ is a DAG-based Byzantine Fault Tolerant consensus protocol that significantly improves commit latency while maintaining high throughput, bridging the gap between latency-optimized and throughput-optimized BFT protocols.

Contribution

Shoal++ introduces a novel DAG BFT protocol that reduces commit latency from 10.5 to 4.5 message exchanges without sacrificing throughput.

Findings

Achieves throughput comparable to state-of-the-art DAG BFT protocols.

Reduces average commit latency by up to 60%.

Maintains high scalability and fault tolerance.

Abstract

Today's practical partially synchronous Byzantine Fault Tolerant (BFT) consensus protocols trade off low latency and high throughput. On the one end, traditional BFT protocols such as PBFT and its derivatives optimize for latency. They require, in fault-free executions, only 3 message exchanges to commit, the optimum for BFT consensus. However, this class of protocols typically relies on a single leader, hampering throughput scalability. On the other end, a new class of so-called DAG-BFT protocols demonstrates how to achieve highly scalable throughput by separating data dissemination from consensus, and using every replica as proposer. Unfortunately, existing DAG-BFT protocols pay a steep latency premium, requiring on average 10.5 message exchanges to commit a transactions. This work aims to soften this tension and proposes Shoal++, a novel DAG-based BFT consensus system that offers the throughput of DAGs while reducing commit latency to an average of 4.5 message exchanges. Our empirical findings are encouraging, showing that Shoal++ achieves throughput comparable to state-of-the-art DAG BFT solutions while reducing latency by up to 60%.