Pipeline Processing of Multi-Way Queries in Shared-Memory Systems

This paper explores the pipeline processing of multi-way join queries using hash-based join algorithm. The basic approach that has been adopted in the literature is: "split" the join tree into segments and for each segment, split each base rela tion into buckets and pipeline the segment using the buckets. The effectiveness of the approach depends on two closely related factors - the number of buckets and the number of segments. We investigate how varying these factors may affect the system performance. Two greedy heuristics, proposed to generate query evalua tion plans with "optimal" pipeline length, are shown to perform best in most cases.