Fission: Autonomous, Scalable Sharding for IoT Blockchain

IoT blockchain suffers heavy performance issues because of the massive transactions generated by various IoT nodes. By dividing nodes into different shards, sharding can produce blocks in parallel and hence improve the throughput of the blockchain system. Unlike the traditional blockchain system, IoT blockchain mainly consists of smart devices and the transactions are usually generated from the real world, such as the sensor data, photos taken by cameras, and so on. In IoT blockchain, closer nodes usually share a lower network latency and the transactions they generate are more related. Therefore, location-based sharding is an effective approach to improve the performance of IoT blockchain. Traditionally, IoT nodes are di-vided into different shards based on geographical locations or the connected edge server. However, the key challenge of sharding in IoT blockchain is how to guarantee the equality of shards division as to the unpredictable distribution and the dynamic behavior of IoT nodes. On one hand, shards can not be pre-divided because we can not predict the number or the distribution of the IoT nodes. On the other hand, nodes continuously joining or quitting shards will also break the equality of the shards division. In this paper, we propose Fission, a sharding mechanism designed for IoT blockchain. Fission divide shards based on the Voronoi diagram without any preknowledge about the nodes distribution, and support dynamic, autonomous sharding adjustment based on distributed Delaunay Triangulation. In addition, Fission uses a new diffusion-based consensus algorithm to achieve the linear scalability of throughput. The experimental results show that Fission can construct and adjust shards at a very low cost and can execute in a decentralized manner. The throughput can reach 1900tps in 500 nodes with only 5M bps bandwidth, and can scale linearly as the nodes increase.