【摘要】 本文重点介绍RXDB查询处理的核心模块——查询优化的设计和实现。优化方法是一种启发式方法,其主要特征是利用相同属性上等连接谓词的传递性将连接分组,对主外码连接使用按GAPS结构组织的主外索引以提高查询处理效率,存取路径的选择采用启发式规则和代价评估相结合的方法,代价计算依据统计信息,并且在局部优化后进行整体优化,以改进优化仅局限于一个查询块所带来的缺点。更多还原

【Abstract】 This paper describes the design and implementation of query optimization for kernal module of query processing in RXDB. The main features of optimization approach, which is a heuristic, are clustering relations using the transitivity rule of the equi-join predicate. In order to enhance the efficiency of query processing primary-foreign index organized by GAPS structure will be used for join between the primary key and foreign key. The access path will be selected through the combination heuristic rule with cost evaluation. Cost evaluation is based on statistical data. The grobal optimization after local optimization processing overcomes the drawbacks that might be caused by optimization confined to single query block.更多还原