Abstract: Sharding is one of the on-chain solutions for blockchain scalability.State sharding can solve the scalability problem of the public chain without reducing security.Each state sharding only maintains a part of the state.There is a certain probability that the proportion of Byzantine nodes will exceed one third in a single sharding,even if the probability of Byzantine nodes is no more than one third in all nodes with PBFT consensus algorithm,resulting in the failure of verifying the consensus.Therefore,the nodes in the sharding need to be reconfigured periodically,and multi-round PBFT consensus verification algorithm with small time slots can effectively solve this problem.However,stateless nodes cannot work effectively,and new nodes need to synchronize the state of the sharding.The state synchronization scheme based on candidate nodes queue for multi-round PBFT consensus verification algorithm is proposed to solve this problem.Nodes that are in synchronized state first enter the queue of candidate nodes,and different candidate nodes are provided for each round of PBFT consensus verification.At the same time,a node gets a corresponding credits based on its historical behavior record during status synchronization to help optimizing the subsequent algorithm.Finally,experiment shows that the proposed scheme not only solves the problem of state synchronization,but also improves the efficiency of consensus verification and the throughput of the system.

Key words: Blockchain, State sharding, State synchronization, Multiple rounds verification, PBFT