Flow Algorithms for Parallel Query Optimization

We address the problem of minimizing the response time of a multi-way join query using pipelined (inter-operator) parallelism, in a parallel or a distributed environment. We observe that in order to fully exploit the parallelism in the system, we must consider a new class of ";interleaving"; plans, where multiple query plans are used simultaneously to minimize the response time of a query (or to maximize the tuple-throughput of the system). We cast the query planning problem in this environment as a ";flow maximization problem";, and present polynomial-time algorithms that (statically) find the optimal set of plans to use for a given query, for a large class of multi-way join queries. Our proposed algorithms also naturally extend to query optimization over web services. Finally we present an extensive experimental evaluation that demonstrates both the need to consider such plans in parallel query processing and the effectiveness of our algorithms.