Query Processing in Distributed Database Systems
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Department of Computer Science and Information Technology
Abstract
Query processing on a distributed database system requires transmission of data
between computers on a communication network. Minimizing the amount of data
transmission is one of the fundamental principles to reduce the query processing cost
and to prevent network congestion.
The semijoin operation is important in formulating query processing strategies.
Semijoin preprocessing strategy provides enough opportunities to significantly reduce
the amount of data required to be transmitted on the network by first reducing the
cardinalities of a distributed relations using semijoins and then transmitting the
resultant relations to the result node.
Algorithm LIGHT which is based on new heuristic for generating semijoin
preprocessing strategies for queries has been developed in this work. Heuristic used in
algorithm LIGHT can be thought as modification of heuristic used in algorithm SDD1.
Simulation model has been constructed to evaluate the performance of existing query
preprocessing algorithm SDD-1 and algorithm LIGHT. This model test random
queries and results are presented and discussed. It is shown that algorithm LIGHT
performs better than algorithm SDD-1 in general.