Abstract: Most existing permissioned blockchain systems adopt serial transaction execution methods,which cannot take advantage of the high performance of multi-core processors.This serial method will be a performance bottleneck in permissioned blockchains with high performance consensus algorithms.To reduce execution time of transactions in permissioned block-chains with order-execute-validate architecture,two transaction concurrency models are proposed.First,an address table-based parallel execution model is proposed that maps the read and write sets of transactions to the address table through static analysis and constructs a scheduling graph using the address table to achieve parallel execution of transactions without data conflicts.Second,a parallel execution model based on a multi-version timestamp ordering algorithm is proposed,in which the leader node uses a multi-version timestamp ordering algorithm to pre-execute transactions in parallel and stores the scheduling graph into the block in the form of transaction dependency triplets.All validation nodes schedule via transaction dependency triplets to achieve parallel execution of transactions under the premise of consistency.Finally,the two parallel transaction execution models designed in this paper are implemented in Tendermint,and a performance experiment during the transaction execution phase and a performance experiment with multiple nodes are conducted.Experimental results show that the above models reduce the transaction execution time by 68.6% and 28.5% with a single node and 8 threads,and increase the blockchain throughput by about 43.4% and 19.5% with 4 peer nodes and 8 threads per node,respectively.

Key words: Blockchain, Practical Byzantine fault tolerance, Transaction concurrency, Multi-version timestamp ordering, Tendermint