August 2009
Intermediate to advanced
893 pages
26h 48m
English
Content preview from Database Systems: Concepts, Design and Applications
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18.5. Distributed Query Processing
In a DDBMS, a query may require data from the databases distributed in more than one site. Some database systems support relation databases whose parts are physically separated. Different relations might reside at different sites, multiple copies of a single relation can be distributed among several sites, or one relation might be partitioned into sub-relations and these sub-relations distributed to multiple sites. In order to evaluate a query issued at a given site, it may be necessary to transfer data between various sites. Therefore, it is important here to optimise on the time required to access such a query, which will be largely comprised of the time spent in transmitting data between sites rather and ...
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