Sharding technologies allow the Internet of Things (IoT) to deploy blockchains in large-scale applications with good scalability. However, conventional sharding strategies in IoT blockchain are highly restricted because most IoT devices are dynamic and heterogeneous. They fail to partition and reconfigure shards with a fine-balanced tradeoff between throughput and security. Therefore, we propose SmartChain, which is a dynamic and self-adaptive sharding framework devised for making sharding decisions on the IoT blockchain featured with dynamics and heterogeneity. Specifically, we elaborate on how SmartChain performs reconfiguration and provide a quantitative analysis of shard performance. We then formulate the long-term tradeoff of throughput and security as a Markov decision process. Considering the nature of time-varying devices (e.g., amount of computing power, location), we develop a Transferable Proximal Policy Optimization (PPO) with Demonstrations algorithm, namely TPPOD, to help quickly reconfigure shards when the environment changes. Thus, based on current state, SmartChain can adaptively and dynamically select shard number, partition structure, and primary selection mode. Evaluations show that SmartChain enables high throughput and low risk of security, and reduces 70% of the training time averaged over baselines. Our implementation of TPPOD is 8.3 times of average system reward compared with the PPO-based sharding strategy with uniform sampling.

中文翻译：

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SmartChain：物联网区块链的动态自适应分片框架

分片技术使得物联网能够在大规模应用中部署区块链，并具有良好的可扩展性。然而，物联网区块链中的传统分片策略受到高度限制，因为大多数物联网设备是动态的和异构的。他们无法在吞吐量和安全性之间进行精细平衡的权衡来分区和重新配置分片。因此，我们提出了SmartChain，这是一种动态、自适应的分片框架，旨在针对具有动态性和异构性的物联网区块链进行分片决策。具体来说，我们详细阐述了 SmartChain 如何执行重新配置，并提供分片性能的定量分析。然后，我们将吞吐量和安全性的长期权衡制定为马尔可夫决策过程。考虑到随时间变化的设备的性质（例如，计算能力、位置），我们开发了一种带有演示算法的可转移近端策略优化（PPO），即TPPOD，以帮助在环境变化时快速重新配置分片。因此，SmartChain可以根据当前状态自适应地动态选择分片数量、分区结构和主选模式。评估表明，SmartChain 可实现高吞吐量和低安全风险，并比基线平均减少 70% 的训练时间。与基于 PPO 的均匀采样分片策略相比，我们实施的 TPPOD 是平均系统奖励的 8.3 倍。