1 / 58

Evolution and Advantages of Distributed Database Systems

Explore the evolution, advantages, and challenges of Distributed Database Management Systems (DDBMS). Learn about centralized and distributed database management, components, characteristics, functions, and more.

christinefoster
Download Presentation

Evolution and Advantages of Distributed Database Systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  5. Centralized Database Management System Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  6. DDBMS Advantages • Data are located near “greatest demand” site • Faster data access • Faster data processing • Growth facilitation • Improved communications • Reduced operating costs • User-friendly interface • Less danger of a single-point failure • Processor independence Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  7. DDBMS Disadvantages • Complexity of management and control • Security • Lack of standards • Increased storage requirements • Greater difficulty in managing the data environment • Increased training cost Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  8. Distributed Processing Environment Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  9. Distributed Database Environment Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  10. Characteristics of Distributed Management Systems • Application interface • Validation • Transformation • Query optimization • Mapping • I/O interface • Formatting • Security • Backup and recovery • DB administration • Concurrency control • Transaction management Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  11. Characteristics of Distributed Management Systems (continued) • Must perform all the functions of a centralized DBMS • Must handle all necessary functions imposed by the distribution of data and processing • Must perform these additional functions transparently to the end user Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

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

  13. DDBMS Components • 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 • 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, 6th Edition, Rob & Coronel

  14. Distributed Database System Components Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

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

  16. 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, 6th Edition, Rob & Coronel

  17. Single-Site Processing, Single-Site Data (Centralized) Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  18. 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, 6th Edition, Rob & Coronel

  19. Multiple-Site Processing, Single-Site Data Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  20. 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, 6th Edition, Rob & Coronel

  21. 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, 6th Edition, Rob & Coronel

  22. Heterogeneous Distributed Database Scenario Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  23. 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, 6th Edition, Rob & Coronel

  24. Distribution Transparency • Allows management of a physically dispersed database as though it were a centralized database • Three levels of distribution transparency are recognized: • Fragmentation transparency • Location transparency • Local mapping transparency Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  25. A Summary of Transparency Features Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  26. Fragment Locations Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  27. Transaction Transparency • Ensures database transactions will maintain distributed database’s integrity and consistency Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  28. Distributed Requests and Distributed Transactions • Distributed transaction • Can update or request data from several different remote sites on a network • Remote request • Lets a single SQL statement access data to be processed by a single remote database processor • Remote transaction • Accesses data at a single remote site Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  29. Distributed Requests and Distributed Transactions (continued) • Distributed transaction • Allows a transaction to reference several different (local or remote) DP sites • Distributed request • Lets a single SQL statement reference data located at several different local or remote DP sites Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  30. A Remote Request Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  31. A Remote Transaction Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  32. A Distributed Transaction Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  33. A Distributed Request Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  34. Another Distributed Request Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  35. 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, 6th Edition, Rob & Coronel

  36. The Effect of a Premature COMMIT Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  37. Two-Phase Commit Protocol • Distributed databases make it possible for a transaction to access data at several sites • Final COMMIT must not be issued until all sites have committed their parts of the transaction • Two-phase commit protocol requires each individual DP’s transaction log entry be written before the database fragment is actually updated Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  38. Performance Transparency and Query Optimization • Objective of query optimization routine is to minimize total cost associated with the execution of a request • Costs associated with a request are a function of the: • Access time (I/O) cost • Communication cost • CPU time cost Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  39. Performance Transparency and Query Optimization (continued) • Must provide distribution transparency as well as replica transparency • Replica transparency: • DDBMS’s ability to hide the existence of multiple copies of data from the user • Query optimization techniques: • Manual or automatic • Static or dynamic • Statistically based or rule-based algorithms Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  40. Distributed Database Design • Data fragmentation: • How to partition the database into fragments • Data replication: • Which fragments to replicate • Data allocation: • Where to locate those fragments and replicas Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  41. Data Fragmentation • Breaks single object into two or more segments or fragments • Each fragment can be stored at any site over a computer network • Information about data fragmentation is stored in the distributed data catalog (DDC), from which it is accessed by the TP to process user requests Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  42. Data Fragmentation 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, 6th Edition, Rob & Coronel

  43. A Sample CUSTOMER Table Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  44. Horizontal Fragmentation of the CUSTOMER Table by State Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  45. Table Fragments in Three Locations Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  46. Vertically Fragmented Table Contents Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  47. Mixed Fragmentation of the CUSTOMER Table Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  48. Data Replication • Storage of data copies at multiple sites served by a computer network • Fragment copies can be stored at several sites to serve specific information requirements • Can enhance data availability and response time • Can help to reduce communication and total query costs Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  49. Table Contents After the Mixed Fragmentation Process Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

  50. Data Replication Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

More Related