M cheung william tan and carson woo 13 busi 335

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Unformatted text preview: ary key, which is common to all fragments BUSI 335 Copyright © 2009-10 Y.M. Cheung, William Tan and Carson Woo 13 BUSI 335 Copyright © 2009-10 Y.M. Cheung, William Tan and Carson Woo 14 Replication Vertical Fragmentation Fragmentation • Example: Employees table may contain many different different fields • Refers to the storage of fragment copies at multiple multiple sites on a network – Fragment #1: Fields relevant to Payroll (Toronto) – Fragment #2: Fields relevant to HR (Vancouver) #2: Fields relevant to HR (Vancouver) – enhances data availability and response time – used to reduce communication and total query costs (subject to update trade-off) • Mutual consistency rule – requires that all copies of data fragments be id identical – DDBMS must ensure that a database update is performed at all sites where replicas exist BUSI 335 Copyright © 2009-10 Y.M. Cheung, William Tan and Carson Woo 15 BUSI 335 Copyright © 2009-10 Y.M. Cheung, William Tan and Carson Woo 16 Replication Trade Replication Trade-Off Summary • Read operations: • Distributed database and distributed database and distributed – determine which replica to access processing • Write operations: • Data fragmentation and replication fragmentation and replication – all replicas must be accessed and updated replicas be accessed and Source: Database Systems by Rob and Coronel BUSI 335 Copyright © 2009-10 Y.M. Cheung, William Tan and Carson Woo 17 BUSI 335 Copyright © 2009-10 Y.M. Cheung, William Tan and Carson Woo 18...
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This document was uploaded on 03/04/2014 for the course COMM 335 at The University of British Columbia.

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