Journal of East China Normal University(Natural Sc

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Optimization strategies of correlated subquery for distributed database

MAO Si-yu, ZHANG Li-jun, ZHANG Xiao-fang, GAO Jin-tao, LI Zhan-huai   

  1. School of Computer, Northwestern Polytechnical University, Xi’an 710129, China
  • Received:2016-06-24 Online:2016-09-25 Published:2016-11-29


A query which occurs in another query as a filter is called subquery, and if the filtering condition of a subquery depends on its parent query, it is called correlated
subquery. Generally, the execution cost of query with correlated subquery is high due to that subquery would be executed multiply, which leads to multiple disk access and extra communications in distributed system. Based on the investigation of the classical optimization strategies of correlated subquery, and according to the characteristics of distributed system, we adopt pulling up subquery, removing useless tree and eliminating aggregation function to optimize correlated subquery in distributed database system. And we implement these strategies in the distributed relational database OceanBase for the correlated subquery predicate EXIST. Experiment results show that these strategies can significantly improve the performance of a correlated subquery.

Key words: distributed database, correlated subquery, subquery optimization