Abstract: Blockchain technology has the characteristics of decentralization and immutability,and is considered to be the next generation of disruptive core technology.However,the existing blockchain system is weak in data management and can only query related transactions according to the hash value.The current research on query mostly stores data synchronously into an external database,and then uses an external database to query,or focuses on how to ensure the reliability of the whole node,but the problem of low query efficiency of blockchain remains unsolved in a practical sense.A new solution is proposed in the paper.First,dividing blockchain data into different attributes.Next,based on different attributes,combining with the Merkle tree of the blockchain and multiple index structures,a new index-MHerkle tree-is proposed to enhance the query performance of the blockchain,while ensuring the immutability of blockchain;Then,the index construction algorithm of MHerkle tree is designed,and the query algorithm based on different attributes and the range query algorithm are proposed according to the index.Finally,experiment shows the feasibility and effectiveness of the proposed index.

Key words: Blockchain, Immutability, Index, Optimization, Query