Query Optimization Techniques of A Shared nothing Parallel Database System
Ji Wen · Chinese Journal of Computers · 2000
Query optimization is the critical technique of parallel database systems. This paper addresses the distinguishing two phase optimization strategy implemented in a shared nothing parallel database system PBASE/2. In order to cut down the enormous search space of parallel query optimization, PBASE/2 divides parallel query processing into two phases, sequential optimization and parallelization. In sequential optimization, PBASE/2 predicts the communication cost of parallel execution, and addes communication cost into cost model. At the same time, the traditional dynamic programming search algorithm is modified and extended. By these mechanisms, it is guaranteed that the sequential minimal cost plan also is the parallel minimal cost plan. The object of parallelization phase is to balance the query work loading among various resources in the system. Thus, a new concept, resources load balancing factor, is put forward. Other techniques such as heuristics, dynamic programming based parallelizaion algorithm, and task scheduling ensure the quality of the outgoing parallel query evaluation plans.