Coloring Away Communication in Parallel Query Optimization

We address the problem of finding parallel plans for SQL queries using the two-phase approach of join ordering and query rewrite (JOQR) followed by parallelization. We focus on the JOQR phase and develop optimization algorithms that account for communication as well as computation costs. Using a model based on representing the partitioning of data as a color, we devise an efficient algorithm for the problem of choosing the partitioning attributes in a query tree so as to minimize total cost. We extend our model and algorithm to incorporate the interaction of data partitioning with conventional optimization choices such as access methods and strategies for computing operators. Our algorithms apply to queries that include operators such as grouping, aggregation, intersection and set difference in addition to joins.