1. Distributed Database Management Systems
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
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)
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

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

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

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

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

55. Data Replication
Storage of data copies at multiple sites served by 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, 7th Edition, Rob & Coronel

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

57. Data Replication (continued)
Replication scenarios
Fully replicated database
Stores multiple copies of each database fragment at multiple sites
Can be impractical due to amount of overhead
Partially replicated database
Stores multiple copies of some database fragments at multiple sites
Most DDBMSs are able to handle the partially replicated database well
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

58. Data Replication (continued)
Replication scenarios (continued)
Unreplicated database
Stores each database fragment at single site
No duplicate database fragments
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

59. Data Allocation Deciding where to locate data Allocation strategies
Centralized data allocation
Entire database is stored at one site
Partitioned data allocation
Database is divided into several disjointed parts (fragments) and stored at several sites
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

60. Data Allocation (continued)
Allocation strategies (continued)
Replicated data allocation
Copies of one or more database fragments are stored at several sites
Data distribution over computer network is achieved through data partition, data replication, or combination of both
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

61. Client/Server vs. DDBMS
Way in which computers interact to form system
Features user of resources, or client, and provider of resources, or server
Can be used to implement a DBMS in which client is the TP and server is the DP
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

62. Client/Server vs. DDBMS (continued)
Client/server advantages
Less expensive than alternate minicomputer or mainframe solutions
Allow end user to use microcomputer’s GUI, thereby improving functionality and simplicity
More people in job market have PC skills than mainframe skills
PC is well established in workplace
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

63. Client/Server vs. DDBMS (continued)
Client/server advantages (continued)
Numerous data analysis and query tools exist to facilitate interaction with DBMSs available in PC market
Considerable cost advantage to offloading applications development from mainframe to powerful PCs
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

64. Client/Server vs. DDBMS (continued)
Client/server disadvantages
Creates more complex environment
Different platforms (LANs, operating systems, and so on) are often difficult to manage
An increase in number of users and processing sites often paves the way for security problems
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

65. Client/Server vs. DDBMS (continued)
Client/server disadvantages (continued)
Possible to spread data access to much wider circle of users
Increases demand for people with broad knowledge of computers and software
Increases burden of training and cost of maintaining the environment
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

66. C. J. Date’s Twelve Commandments for Distributed Databases
Local site independence
Central site independence
Failure independence
Location transparency
Fragmentation transparency
Replication transparency
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

67. C. J. Date’s Twelve Commandments for Distributed Databases (continued)
Distributed query processing
Distributed transaction processing
Hardware independence
Operating system independence
Network independence
Database independence
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

68. Summary
Distributed database stores logically related data in two or more physically independent sites connected via computer network
Distributed processing is division of logical database processing among two or more network nodes
Distributed databases require distributed processing
Main components of DDBMS are transaction processor and data processor
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

69. Summary (continued)
Current database systems can be classified by extent to which they support processing and data distribution
Homogeneous distributed database system integrates only one particular type of DBMS over computer network
Heterogeneous distributed database system integrates several different types of DBMSs over computer network
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

70. Summary (continued)
DDBMS characteristics are best described as set of transparencies
Transaction is formed by one or more database requests
Distributed concurrency control is required in network of distributed databases
Distributed DBMS evaluates every data request to find optimum access path in distributed database
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel

71. Summary (continued)
The design of distributed database must consider fragmentation and replication of data
Database can be replicated over several different sites on computer network
Client/server architecture refers to way in which two computers interact over computer network to form a system
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel