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Chapter 12

Chapter 12. Distributed Database Management Systems Database Systems: Design, Implementation, and Management, Seventh Edition, Rob and Coronel. In this chapter, you will learn:. What a distributed database management system (DDBMS) is and what its components are

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Chapter 12

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  1. Chapter 12 Distributed Database Management Systems Database Systems: Design, Implementation, and Management, Seventh Edition, Rob and Coronel

  2. 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, 7th Edition, Rob & Coronel

  3. 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, 7th Edition, Rob & Coronel

  4. 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 spawned a demand for applications based on data access from different sources at multiple locations Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  5. The Evolution of Distributed Database Management Systems (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  6. DDBMS Advantages and Disadvantages • Advantages include: • Data are located near “greatest demand” site • Faster data access • Faster data processing • Growth facilitation • Improved communications Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  7. DDBMS Advantages and Disadvantages (continued) • Advantages include (continued): • Reduced operating costs • User-friendly interface • Less danger of a single-point failure • Processor independence Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  8. DDBMS Advantages and Disadvantages (continued) • Disadvantages include: • Complexity of management and control • Security • Lack of standards • Increased storage requirements • Increased training cost Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  9. DDBMS Advantages and Disadvantages (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  10. DDBMS Advantages and Disadvantages (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  11. DDBMS Advantages and Disadvantages (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  12. Characteristics of Distributed Management Systems • Application interface • Validation • Transformation • Query optimization • Mapping • I/O interface Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  13. Characteristics of Distributed Management Systems (continued) • Formatting • Security • Backup and recovery • DB administration • Concurrency control • Transaction management Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  14. Characteristics of Distributed Management Systems (continued) • Must perform all the functions of centralized DBMS • Must handle all necessary functions imposed by distribution of data and processing • Must perform these additional functions transparently to the end user Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  15. Characteristics of Distributed Management Systems (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  16. DDBMS Components • Must include (at least) the following components: • Computer workstations • Network hardware and software • Communications media • Transaction processor (application processor, transaction manager) • Software component found in each computer that requests data Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  17. DDBMS Components (continued) • Must include (at least) the following components (continued): • 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, 7th Edition, Rob & Coronel

  18. DDBMS Components (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

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

  20. 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 system Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  21. Single-Site Processing, Single-Site Data (SPSD) (continued) • Typical of most mainframe and midrange computer DBMSs • DBMS is located on host computer, which is accessed by dumb terminals connected to it • Also typical of first generation of single-user microcomputer databases Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  22. Single-Site Processing, Single-Site Data (SPSD) (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  23. Multiple-Site Processing, Single-Site Data (MPSD) • Multiple processes run on different computers sharing single data repository • MPSD scenario requires network file server running conventional applications that are accessed through LAN • Many multiuser accounting applications, running under personal computer network, fit such a description Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  24. Multiple-Site Processing, Single-Site Data (MPSD) (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  25. 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, 7th Edition, Rob & Coronel

  26. 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, 7th Edition, Rob & Coronel

  27. Multiple-Site Processing, Multiple-Site Data (MPMD) (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  28. Distributed Database Transparency Features • Allow end user to feel like database’s only user • Features include: • Distribution transparency • Transaction transparency • Failure transparency • Performance transparency • Heterogeneity transparency Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  29. Distribution Transparency • Allows management of physically dispersed database as though it were a centralized database • Following three levels of distribution transparency are recognized: • Fragmentation transparency • Location transparency • Local mapping transparency Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  30. Distribution Transparency (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  31. Distribution Transparency (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  32. Transaction Transparency • Ensures database transactions will maintain distributed database’s integrity and consistency Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  33. Distributed Requests and Distributed Transactions • Distributed transaction • Can update or request data from several different remote sites on network • Remote request • Lets single SQL statement access data to be processed by single remote database processor • Remote transaction • Accesses data at single remote site Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  34. Distributed Requests and Distributed Transactions (continued) • Distributed transaction • Allows transaction to reference several different (local or remote) DP sites • Distributed request • Lets single SQL statement reference data located at several different local or remote DP sites Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  35. Distributed Requests and Distributed Transactions (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  36. Distributed Requests and Distributed Transactions (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  37. Distributed Requests and Distributed Transactions (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  38. Distributed Requests and Distributed Transactions (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  39. Distributed Requests and Distributed Transactions (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  40. Distributed Concurrency Control • Multisite, multiple-process operations are much more likely to create data inconsistencies and deadlocked transactions than are single-site systems Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  41. Distributed Concurrency Control (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  42. Two-Phase Commit Protocol • Distributed databases make it possible for transaction to access data at several sites • Final COMMIT must not be issued until all sites have committed their parts of transaction • Two-phase commit protocol requires each individual DP’s transaction log entry be written before database fragment is actually updated Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  43. Performance Transparency and Query Optimization • Objective of query optimization routine is to minimize total cost associated with execution of request • Costs associated with request are function of: • Access time (I/O) cost • Communication cost • CPU time cost • Must provide distribution transparency as well as replica transparency Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  44. Performance Transparency and Query Optimization (continued) • Replica transparency • DDBMS’s ability to hide existence of multiple copies of data from user • Query optimization techniques include: • Manual or automatic • Static or dynamic • Statistically based or rule-based algorithms Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  45. Distributed Database Design • Data fragmentation • How to partition database into fragments • Data replication • Which fragments to replicate • Data allocation • Where to locate those fragments and replicas Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  46. Data Fragmentation • Breaks single object into two or more segments or fragments • Each fragment can be stored at any site over computer network • Information about data fragmentation is stored in distributed data catalog (DDC), from which it is accessed by TP to process user requests Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  47. Data Fragmentation (continued) • Strategies • Horizontal fragmentation • Division of a relation into subsets (fragments) of tuples (rows) • Vertical fragmentation • Division of a relation into attribute (column) subsets • Mixed fragmentation • Combination of horizontal and vertical strategies Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  48. Data Fragmentation (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  49. Data Fragmentation (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

  50. Data Fragmentation (continued) Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

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