Optimization of Multi-Way Join Queries for Parallel Execution

Most of the existing relational database query optimizers generate multi-way join plans only from those linear ones to reduce the optimization overhead. For multiprocessor computer systems, this strategy seems inadequate since it may reduce the search space too much to generate near-optimal plans. In this paper we present a framework for optimization of multiway join queries in multiprocessor computer systems. The optimization process not only determines the order and method in which each join should be performed, but also determines the number of joins should be executed in parallel, and the number of processors should be allocated to each join. The preliminary performance study shows that the optimizer usually generate optimal or near-optimal plans when the number of joins is relatively small. Even when the number of joins increases, the algorithm still gives reasonably good performance. Furthermore, the optimization overhead is much lesser compared to exhaustive search.