Algorithms to Process Distributed Queries in Fast Local Networks
IEEE Transactions on Computers
Optimizing Joins in Fragmented Database Systems on a Broadcast Local Network
IEEE Transactions on Software Engineering
Optimizing equijoin queries in distributed databases where relations are hash partitioned
ACM Transactions on Database Systems (TODS)
Outerjoin optimization in multidatabase systems
DPDS '90 Proceedings of the second international symposium on Databases in parallel and distributed systems
On the Complexity of Distributed Query Optimization
IEEE Transactions on Knowledge and Data Engineering
A Parallel Execution Method for Minimizing Distributed Query Response Time
IEEE Transactions on Parallel and Distributed Systems
Performance Issues in Distributed Query Processing
IEEE Transactions on Parallel and Distributed Systems
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The problem of optimal query processing in distributed database systems was shown to be NP-hard. However, for a special type of queries called star queries, we have developed a polynomial optimal algorithm. Semijoin tactics are applied for query processing. An execution graph is introduced to represent the semijoin programs associated with the distributed processing of the queries. We then identify optimality properties of semijoin programs for star queries, and use these properties to derive the optimal semijoin program. We have shown that the optimal semijoin program can be found from serial semijoin strategies, defined as serial semijoin programs which include each semijoin associated with the query exactly once. By making certain assumptions on the file sizes and the semijoin selectivities, we can obtain the optimal semijoin program from these strategies in polynomial time. Our assumption on selectivites is consistent in the sense that we consider the selectivity of a semijoin based on the current database state, i.e., we take into consideration the reduction effects of all prior semijoins.