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ch22 - Chapter22: ,5thEd Silberschatz,KorthandSudarshan...

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Database System Concepts, 5th Ed . © Silberschatz, Korth and Sudarshan See  www.db-book.com  for conditions on re-use  Chapter 22: Distributed Databases Chapter 22: Distributed Databases
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© Silberschatz, Korth and Sudarshan 22.<number> Database System Concepts - 5 th  Edition, Aug 22,  2005. Chapter 22: Distributed Databases Chapter 22: Distributed Databases Heterogeneous and Homogeneous Databases Distributed Data Storage Distributed Transactions Commit Protocols Concurrency Control in Distributed Databases Availability Distributed Query Processing Heterogeneous Distributed Databases Directory Systems
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© Silberschatz, Korth and Sudarshan 22.<number> Database System Concepts - 5 th  Edition, Aug 22,  2005. Distributed Database System Distributed Database System A distributed database system consists of loosely coupled sites that share  no physical component Database systems that run on each site are independent of each other Transactions may access data at one or more sites
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© Silberschatz, Korth and Sudarshan 22.<number> Database System Concepts - 5 th  Edition, Aug 22,  2005. Homogeneous Distributed Databases Homogeneous Distributed Databases In a homogeneous distributed database All sites have identical software  Are aware of each other and agree to cooperate in processing user  requests. Each site surrenders part of its autonomy in terms of right to change  schemas or software Appears to user as a single system In a heterogeneous distributed database Different sites may use different schemas and software Difference in schema is a major problem for query processing Difference in software is a major problem for transaction  processing Sites may not be aware of each other and may provide only  limited facilities for cooperation in transaction processing
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© Silberschatz, Korth and Sudarshan 22.<number> Database System Concepts - 5 th  Edition, Aug 22,  2005. Distributed Data Storage Distributed Data Storage Assume relational data model Replication System maintains multiple copies of data, stored in different sites,  for faster retrieval and fault tolerance. Fragmentation Relation is partitioned into several fragments stored in distinct sites Replication and fragmentation can be combined Relation is partitioned into several fragments: system maintains  several identical replicas of each such fragment.
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© Silberschatz, Korth and Sudarshan 22.<number> Database System Concepts - 5 th  Edition, Aug 22,  2005.
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