System from optimizing query processing of multi-attribute distributed relations using local relation tuple numbers to choose semijoins

摘要

A distributed database system includes a communication network having a plurality of nodes each with a distributed database, a local process part for extracting relations from each database by performing local processes at each node when a query including multi-attribute relations thereof is input, a degree setting part for setting a degree number of each of the extracted relations, a relation set part for arranging relation sets each containing relations having the same degree number by grouping the extracted relations according to the degree number, an extraction part for extracting single-attribute relations from each relation set so that the single-attribute relations are added to a first relation set having the lowest degree number, a semijoin operating part for repeatedly semijoining two relations of a only relation set only when the quantity of transfer data resulting from the semijoining is decreased, so that a derived relation is added to a next relation set, and a control part for allowing the semijoin operating part to sequentially perform the semijoining and adding so that each derived relation is added to the transfer data.