Fountain: DAG-Based Separate BFT Consensus Made Hashgraph Practical

The limited transaction throughput performance is the primary challenge for single-chain structure blockchain in practical applications. Directed acyclic graph (DAG) technology offers a novel topological structure, significantly improving blockchain’s ability to process massive transactions by containing numerous blocks in a parallel way. However, the existing parallel-chain schemes embed DAG into the Practical Byzantine Fault Tolerance (PBFT) protocol stages to expand the instance, which requires an extent of overall synchronization between multiple chains. Overall consensus synchronously among all parallel chains may delay the system’s progress, particularly when the graph structure is unevenly distributed. This paper introduces a new DAG-based blockchain named Fountain, which aims to provide a loosely coupled consensus algorithm based on the classic parallel-chain scheme Hashgraph. The Fountain scheme changes consensus finality from an overall behavior to a separate behavior, thereby reducing block commit latency from the perspective of each parallel chain. Theoretical analysis reveals that our scheme maintains the same security level as Hashgraph, while experimental simulations demonstrate its effectiveness in optimizing commit latency.