Hierarchical Query Execution in a Parallel Object-Oriented Database System

Abstract We present a hierarchical query execution strategy for a parallel object-oriented database (OODB) system. The system, named PRACTIC, is based on a concurrent active class management model and is mapped to an abstract hierarchical multiprocessor architecture. The proposed strategy is studied analytically and by simulation on a transputer-based machine, verifying the theoretical results. Although the analysis suits both main-memory and disk-based database systems, it becomes significant for main-memory systems where the multiprocessor initialization and communication overheads are comparable to the actual workload. The hierarchical query execution strategy is proved much better than the usual flat strategy of parallel database systems, except some clearly identified extreme cases, where flat processing is better. Furthermore, we propose a declustering scheme for space optimization to improve processor utilization and single-class query performance, by having different classes share memory and computation power of neighboring processing elements.