The Research Of Sharding Scale And Effectiveness With Multi-round PBFT Verification

Blockchain is a distributed ledger used to record transactions,ledger is shared and maintained between participating nodes by using cryptography and has the characteristics of tamper resistance,traceability and decentralization.However,the current blockchain is facing the problem of scalability.In order to solve this problem,scholars at home and abroad have proposed many solutions.Sharding technology is considered to be a key technology that can effectively solve the problem of scalability without reducing the degree of decentralization,PBFT consensus is a proven strong consistency deterministic consensus algorithm,but there is a contradiction between the validation effectiveness and the sharding capacity after adopting PBFT consensus in shard.After sharding,the Byzantine nodes are also allocated into each shard,due to the uneven distribution of Byzantine nodes,the number of Byzantine nodes in a single shard may exceed 1/3,and the validity of the sharding data cannot be verified,causing the validation interrupt problem,which in turn affects the verification effectiveness 'of the entire blockchain At the same time,when nodes are randomly allocated to shards,they face the problems ofuneven distribution and the results of allocation are predicted by dishonest nodes in advance,increasing the probability of Byzantine nodes gathering in the same shard.Therefore,it is necessary to adopt a safe and effective node random assignment algorithm.The main work of this paper is as follows:(1)This paper analyzes the dilemma faced by the current blo ckchain scalability problems,analyzes the advantages and disadvantages of current mainstream scalability solutions,and summarizes the current research of sharding techno logy and the application ofrandom numbers in blockchain.with our discovery,that after the adoption of the PBFT consensus algorithm used in sharding.It may cause that the proportion of the Byzantine nodes in shards are greater than or equal to one-third,which leads to the decrease of validation effectiveness within the shards,resulting in the contradiction between the validation effectiveness and the sharding capacity.The paper quantifies the probability of failure of a single shard and the probability of normal operation of all shards,revealing the seriousness of the problem.(2)Basing onthe understanding ofthe existing blockchain sharding scheme,aiming at the problem of the contradiction between the validation effectiveness and the sharding capacity using PBFT consensus in sharding,a multi-round PBFT verification scheme(MRPV)was proposed in this paper,and a random node allocation algorithm adapted to the multi-round scheme was used.The idea of the MRPV scheme is that when a transaction in the shards fails to reach a result,the random node allocation scheme is called,a new set of nodes is allocated to making a new round of consensus on this transaction until the transaction is verified or the round limit is reached.(3)In the laboratory simulation environment,this paper carried out the experiment of the average number of rounds,the experiment of the rounds difference between the best case and the actual case,the experiment of the probability of the node being assigned to the same shard in two continuous consensus process,and then compare the Elastico sharding scheme,Omniledger sharding scheme,and MRPV scheme from two aspects of average TPS and verification effectiveness of a single shard.The experimental results show that the MRPV scheme improves transaction verification efficiency and thus improves TPS ofthe whole block chain by reducing resubmission and sacrificing certain transaction delay confirmation.