Optimization of correlate subquery based on distributed database

基于分布式数据库的相关子查询优化

¹ School of Computer Science, Northwestern Polytechnical University, Xi’an 710072, China
² Bank of Communications, Shanghai 200120, China

Received: 25 November 2020

Abstract

Subquery is widely used in database. It can be divided into related subquery and non-related subquery according to whether it is dependent on the table of the parent query. For related subqueries, it is necessary to take a tuple from the parent query before executing the subquery, that is, the content of the subquery needs to be repeatedly operated. Disk access costs of this strategy is very big, in the distributed database, because of data communication overhead, in the parent query yuan set is too low efficiency, therefore, for the class sub queries, on the basis of the optimization of the existing query strategy, combining with the characteristics of distributed database, put forward by the subquery on to join queries, eliminate redundant clauses in the subquery, eliminate accumulation function method based on distributed database query optimization strategy, and the effectiveness of the present optimization strategy is verified by experiment.

摘要

子查询在数据库中的应用较为广泛，根据是否与父查询的表有依赖关系，可以将其分为相关子查询和非相关子查询。相关子查询需要先从父查询中取出一个元组后执行子查询，即需要反复对子查询的内容进行运算。这种策略的磁盘访问开销很大，在分布式数据库中，由于存在数据通信开销，在父查询元组过多时效率较低。针对该类子查询，在现有的优化查询策略的基础上，结合分布式数据库的特点，提出了通过子查询上拉为连接查询，消除子查询中冗余子句，消除聚集函数等方法实现的基于分布式数据库的子查询优化策略，并通过实验验证了所提优化策略的有效性。