Abstract: With the rapid growth of application data and the continued development of distributed database systems, data storage in physical independent nodes has become a trend. In this trend, when the application needs to perform complex join queries, it inevitably generates a lot of network traffic. Therefore, improving the efficiency of join query in distributed system is a hot topic. Based on the analysis of the nested loop join, Hash join, semi-join in the OceanBase, this paper puts forward the optimization idea of using hardware resources reasonably and using multithread to execute join operations in parallel. We implement experiment on OceanBase with nested loop join algorithm, Hash join algorithm, semi-join algorithm respectively. The experimental results confirm that the efficiency of join algorithm is positively related to parallelism in a certain number of threads.

Key words: query, semi-join, OceanBase, parallel join