一种启发式异构分布式数据库的查询优化方法

目的提高异构分布式数据库的直询处理速度．方法提出了一个求异构分布式数据库查询处理中，使网上数据传输量达到最小的连接与半连接执行序列的启发式算法．该算法通过一个系列启发式规则，在搜索空间中，选择最有希望的节点作为下一个被扩展的节点，以减少搜索的节点数．结果提出了有用半连接的概念，虽然有的半连接就其本身讲是无益的，但是与一系列连接结合起来使用却是有益的，结论该方法能提高分布式数据库的查询处理速度，尤其在广域网上效果更为明显．

A Heuristic Method for Heterogeneous Distributed Database Query Optimization

Aim To improve the query processing of heterogeneous distributed database. Methods An approach were explored to get join and semijoin sequences which mini- mize the amount of data transmission required for heterogeneous distributed query pro- cessing. The algorithm selected the most hopeful node as next expended node in a search space through using a lot of heuristic rules, which minimized the amount of node searched. Results An important concept was proposed which occur with the use of join operations as reducers in query processing, namely, useful semijoin. Some nonprofitable semijoin, though not profitable in themselves, become profitable owing to the use of subsequent join operations. Conclusion This method can improve the que- ry processing distributed database, specially on WAN.