HIERARCHICAL QUERY EXECUTION IN A PARALLEL OBJECT-ORIENTED DATABASE SYSTEM

We present a hierarchical query execution strategy for a parallel obje ct-oriented database (OODB) system. The system, named PRACTIC, is base d on a concurrent active class management model and is mapped to an ab stract hierarchical multiprocessor architecture. The proposed strategy is studied analytically and by simulation on a transputer-based machi ne, verifying the theoretical results. Although the analysis suits bot h main-memory and disk-based database systems, it becomes significant for main-memory systems where the multiprocessor initialization and co mmunication overheads are comparable to the actual workload. The hiera rchical query execution strategy is proved much better than the usual flat strategy of parallel database systems, except some clearly identi fied extreme cases, where flat processing is better. Furthermore, we p ropose a declustering scheme for space optimization to improve process or utilization and single-class query performance, by having different classes share memory and computation power of neighboring processing elements.