Chapter 19: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 Database System Concepts-6th Edition 19.2 @Silberschatz,Korth and Sudarshan
Database System Concepts - 6 19.2 ©Silberschatz, Korth and Sudarshan th Edition Chapter 19: 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
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 Database System Concepts-6th Edition 19.3 @Silberschatz,Korth and Sudarshan
Database System Concepts - 6 19.3 ©Silberschatz, Korth and Sudarshan th Edition 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
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 Database System Concepts-6th Edition 19.4 @Silberschatz,Korth and Sudarshan
Database System Concepts - 6 19.4 ©Silberschatz, Korth and Sudarshan th Edition 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
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. Database System Concepts-6th Edition 19.5 @Silberschatz,Korth and Sudarshan
Database System Concepts - 6 19.5 ©Silberschatz, Korth and Sudarshan th Edition 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
Data Replication A relation or fragment of a relation is replicated if it is stored redundantly in two or more sites. Full replication of a relation is the case where the relation is stored at all sites. Fully redundant databases are those in which every site contains a copy of the entire database. Database System Concepts-6th Edition 19.6 @Silberschatz,Korth and Sudarshan
Database System Concepts - 6 19.6 ©Silberschatz, Korth and Sudarshan th Edition Data Replication A relation or fragment of a relation is replicated if it is stored redundantly in two or more sites. Full replication of a relation is the case where the relation is stored at all sites. Fully redundant databases are those in which every site contains a copy of the entire database