Distributed ledger technology such as blockchain is considered essential for supporting large numbers of micro-transactions in the Machine Economy, which is envisioned to involve billions of connected heterogeneous and decentralized cyber-physical systems. This stresses the need for performance and scalability of distributed ledger technologies. Sharding divides the blockchain network into multiple committees and is a common approach to improve scalability. However, with current sharding approaches, costly cross-shard verification is needed to prevent double-spending. This paper proposes a novel and more scalable distributed ledger method named ScaleGraph that implements dynamic sharding by using routing and logical proximity concepts from distributed hash tables. ScaleGraph addresses cyber security in terms of integrity, availability, and trust, to support frequent micro-transactions between autonomous devices. Benefits of ScaleGraph include a total storage space complexity of O(t), where t is the global number of transactions (assuming a constant replication degree). This space is sharded over n nodes so that each node needs O(t/n) storage, which provides a high level of concurrency and data localization as compared to other delegated consensus proposals. ScaleGraph allows for a dynamic grouping of validators which are selected based on a distance metric. We analyze the consensus requirements in such a dynamic setting and show that a synchronous consensus protocol allows shards to be smaller than an asynchronous one, and likely yields better performance. Moreover, we provide an experimental analysis of security aspects regarding the required size of the consensus groups with ScaleGraph. Our analysis shows that dynamic sharding based on proximity concepts brings attractive scalability properties in general, especially when the fraction of corrupt nodes is small.

翻译：区块链等分布式账本技术被认为是支持机器经济中大量微交易的关键技术，机器经济预计将涉及数十亿互联的、异构的、去中心化的信息物理系统。这凸显了对分布式账本技术性能和可扩展性的迫切需求。分片技术将区块链网络划分为多个委员会，是提升可扩展性的常用方法。然而，现有的分片方法需要昂贵的跨分片验证来防止双花攻击。本文提出了一种新颖且更具可扩展性的分布式账本方法 ScaleGraph，该方法利用分布式哈希表中的路由和逻辑邻近概念实现动态分片。ScaleGraph 从完整性、可用性和信任度三个方面解决网络安全问题，以支持自主设备间频繁的微交易。ScaleGraph 的优势包括总存储空间复杂度为 O(t)，其中 t 为全局交易总数（假设复制度恒定）。该存储空间被分片到 n 个节点上，因此每个节点仅需 O(t/n) 的存储空间，与其他委托共识方案相比，这提供了更高的并发性和数据本地化程度。ScaleGraph 支持基于距离度量动态选择验证节点并进行分组。我们分析了这种动态设置下的共识要求，并证明同步共识协议允许分片规模小于异步共识协议，且可能获得更好的性能。此外，我们对 ScaleGraph 共识组所需规模的安全性问题进行了实验分析。我们的分析表明，基于邻近概念的动态分片总体上具有优越的可扩展性，尤其在恶意节点比例较低时表现更为突出。