SmartChain: A Dynamic and Self-Adaptive Sharding Framework for IoT Blockchain

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.