ElasticDAG:弹性图式区块链

ElasticDAG:Elastic DAG-based Blockchain

图式区块链采用有向无环图(directed acyclic graph,DAG)的并行拓扑结构,相较于基于串行拓扑结构的传统链式区块链,能够显著提升系统性能,已受到业界广泛关注.然而,现有图式区块链的共识协议与存储模型高度耦合,缺乏灵活性,难以适应多元化应用需求.同时,大部分图式区块链在共识协议层面上缺乏灵活性,局限于概率性共识协议,难以兼顾确认延迟和安全性,尤其对于延迟敏感型应用很不友好.为此,提出弹性图式区块链系统ElasticDAG,其核心思想是将存储模型和共识协议进行解耦,让两者并行、独立地运行,从而灵活适配多元化应用.针对提升系统吞吐量和活性的需求,为存储模型设计自适应区块确认策略和基于划分的确认区块排序算法;针对降低交易确认延迟的需求,设计低延迟DAG区块链混合共识协议.实验结果表明,ElasticDAG原型系统在广域网下的吞吐量高达11 Mb/s,并具有10秒级确认性能.与OHIE相比,Elastic DAG在实现同等吞吐量的情况下,可将确认延迟降低17倍;与Haootia相比,Elastic DAG在实现同等共识延迟的情况下,可将安全性从91.04%提升到99.999914%.

A directed acyclic graph(DAG)-based blockchain adopts a parallel topology and can significantly improve system performance compared with conventional chain-based blockchains with a serial topology.As a result,it has attracted wide attention from the industry.However,the storage model and the consensus protocol of the existing DAG-based blockchains are highly coupled,which lacks the flexibility to meet diversified application demands.Furthermore,most DAG-based blockchains lack flexibility at the consensus protocol level and are limited to probabilistic consensus protocols,which is difficult to take into account confirmation latency and security and is especially unfriendly to delay-sensitive applications.Therefore,this study presents the elastic DAG-based blockchain,namely ElasticDAG.The core idea is to decouple the storage model and the consensus protocol,enabling them to proceed in parallel and independently,so as to flexibly adapt to diversified applications.In order to improve the throughput and activity of the system,an adaptive block confirmation strategy and an epoch-based block ordering algorithm are designed for the storage model.In response to the need to reduce transaction confirmation latency,a low-latency DAG blockchain hybrid consensus protocol is designed.Experimental results demonstrate that the ElasticDAG prototype in WAN can achieve a throughput exceeding 11 Mb/s,and it yields a confirmation latency of tens of seconds.Compared with OHIE and Haootia,ElasticDAG can reduce confirmation latency by 17 times and improve security from 91.04%to 99.999914%while maintaining the same throughput and consensus latency.