10 Chapter 10 Distributed Database Management Systems Database

10 Chapter 10 Distributed Database Management Systems Database Systems: Design, Implementation, and Management, Sixth Edition, Rob and Coronel Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel

10 In this chapter, you will learn: • What a distributed database management system (DDBMS) is and what its components are • How database implementation is affected by different levels of data and process distribution • How transactions are managed in a distributed database environment • How database design is affected by the distributed database environment Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 2

10 10. 1 The Evolution of Distributed Database Management Systems • Distributed database management system (DDBMS) – Governs storage and processing of logically related data over interconnected computer systems in which both data and processing functions are distributed among several sites Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 3

10 The Evolution of Distributed Database Management Systems (continued) • Centralized database required that corporate data be stored in a single central site • Dynamic business environment and centralized database’s shortcomings (i. e. fell short when quickly moving events required faster response times and equally quick access to information) spawned a demand for applications based on data access from different sources at multiple locations Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 4

10 Centralized Database Management What was needed was System quick, un-structured access to databases, using ad hoc queries to generate on-the-spot information Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 5

10 Social and Technological Changes in 1980’s that affected database development an design • Business operations become more decentralized geographically • Competition increased at the global level • Customer demands and market needs favored a decentralized management style • Rapid technological change of low-cost microcomputers. Corporations adopted LAN (Local Area Network) as the basis of their computerized solutions. • The large number of applications based on DBMSs and the need to protect investments in centralized DBMS software made the notion of data sharing attractive Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 6

10 Social and Technological Changes in 1980’s that affected database development an design • Two database requirements became obvious in 1980’s: – Rapid ad hoc data access – Decentralized multiple-access and multiple-location databases • The factors in 1980’s were even more firmly entrenched in 1990’s by: – The growing acceptance of Internet as the platform for data access and distribution – The increased focus on data analysis that led to data mining and data warehouse Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 7

10 Problems of Centralized Database Management • Performance degradation due to a growing number of remote locations over greater distances • High costs associated with maintaining and operating large central database systems • Reliability problems created by dependence on a central site Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 8

10. 2 DDBMS Advantages 10 • Data are located near “greatest demand” site • Faster data access • Faster data processing: able to process data at several sites, spreading out the system’s workload • Growth facilitation • Improved communications • Reduced operating costs • User-friendly interface • Less danger of a single-point failure • Processor independence Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 9

10 10. 3 DDBMS Disadvantages • Complexity of management and control • Security • Lack of standards – transaction management, concurrency control, security, backup, recovery, query optimization, access path selection, etc. • Increased storage requirements • Greater difficulty in managing the data environment • Increased training cost Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 10

10. 4 Distributed Processing and Distributed 10 Databases A database’s logical processing is shared among several physically independent sites connected through a network Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 11

10 Distributed Database Environment Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 12

10 10. 5 Characteristics of Distributed Database Management Systems • A DDBMS must have at least the following functions – Application interface – Validation to analyze data requests – Transformation to determine which request components are distributed and which are local – Query optimization – Mapping – I/O interface – Formatting – Security – Backup and recovery – DB administration – Concurrency control – Transaction management Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 13

10 Characteristics of Distributed Management Systems (continued) • Must perform all the functions of a centralized DBMS 1. 2. 3. 4. 5. 6. 7. 8. Receive an application’s request Validate, analyze, and decompose the request Map the request’s logical-to-physical data components Decompose the request into several disk I/O operations Search for, locate, read, and validate the data Ensure database consistency, security, and integrity Validate the data for the conditions specified by the request Present the selected data in the required format • Must handle all necessary functions imposed by the distribution of data and processing • Must perform these additional functions transparently (透通) to the end user Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 14

10 A Fully Distributed Database Management System Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 15

10. 6 DDBMS Components 10 • Must include (at least) the following components: – Computer workstations – Network hardware and software – Communications media – Transaction processor (or, application processor, or transaction manager) • Software component found in each computer that requests data. It receives and processes the application’s data requests (remote and local). – Data processor or data manager • Software component residing on each computer that stores and retrieves data located at the site • May be a centralized DBMS Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 16

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10 Communication among TPs and DPs • Communication among TPs and DPs is through a specific set of protocols used by the DDBMS. The protocols determine how the DDBMS will: – Interface the network to transport data and commands between DPs and TPs – In TP, synchronize all data received from DPs – In DP, route retrieved data to the appropriate TPs – Ensure common DB functions in a distributed system Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 18

10 10. 7 Levels of Data and Process Distribution Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 19

10 Single-Site Processing, Single-Site Data (SPSD) • All processing is done on single CPU or host computer (mainframe, midrange, or PC) • All data are stored on host computer’s local disk • Processing cannot be done on end user’s side of the system • Typical of most mainframe and midrange computer DBMSs • DBMS is located on the host computer, which is accessed by dumb terminals connected to it • Also typical of the first generation of single-user microcomputer databases Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 20

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10 Multiple-Site Processing, Single-Site Data (MPSD) • Multiple processes run on different computers sharing a single data repository • MPSD scenario requires a network file server running conventional applications that are accessed through a LAN • Many multi-user accounting applications, running under a personal computer network, fit such a description Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 22

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10 Multiple-Site Processing, Single-Site Data • TP acts as a redirector to route all data requests to the file server • The end user sees the file server as just another hard disk • The end user must make a direct reference to the file server to access remote data • All data selection, search, and update functions take place at the workstation, thus requiring the entire file travel through the network for processing at the workstation • A variation is known as Client/Server architecture – All database processing is done at the server site, thus reducing the network traffic Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 24

10 Multiple-Site Processing, Multiple-Site Data (MPMD) • Fully distributed database management system with support for multiple data processors and transaction processors at multiple sites • Classified as either homogeneous or heterogeneous • Homogeneous DDBMSs – Integrate only one type of centralized DBMS over a network Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 25

10 Multiple-Site Processing, Multiple-Site Data (MPMD) (continued) • Heterogeneous DDBMSs – Integrate different types of centralized DBMSs over a network • Fully heterogeneous DDBMS – Support different DBMSs that may even support different data models (relational, hierarchical, or network) running under different computer systems, such as mainframes and microcomputers Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 26

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10 Example Restrictions for Heterogeneous DDBMS • Remote access is read-only and does not support write privileges • Restricted number of remote tables that may be accessed in a single transaction • Restricted number of distinct databases that may be accessed • Restrictions on the database model that may be accessed. • And others Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel 28