In this paper, we explore an approach of interleaving a bushy execution tree with hash filters to improve the execution of multi-join queries. The effect of hash filters is evaluated first. Then, an efficient scheme to determine an effective sequence of hash filters for a bushy execution tree is developed, where hash filters are built and applied based on the join sequence specified in the bushy tree so that not only is the reduction effect optimized but also the cost associated is minimized. Various schemes using hash filters ace implemented and evaluated via simulation. It is experimentally shown that the application of hash filters is in general a very powerful means to improve the execution of multi-join queries, and the improvement becomes more prominent as the number of relations in a query increases.
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