1. Distributed Database Management Systems
Chapter 10
Distributed Database Management Systems
Database Systems: Design, Implementation, and Management, Fifth 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, 5th Edition, Rob & Coronel

3. Evolution of DDBMS Decentralized database management systems (DDBMS)
Interconnected computer systems
Data/processing functions reside on multiple sites
1970’s: Centralized DBMS
1980’s: Social and Technical Changes
Ad hoc capability required
Decentralized management structure common
1990’s: New forces
Internet and the World Wide Web used for data access and distribution
Data analysis through data mining and data warehousing
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

4. DDBMS Advantages Data located near site with greatest demand
Faster data access
Faster data processing
Growth facilitation
Improved communications
Reduced operating costs
User-friendly interface
Less danger of single-point failure
Processor independence
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

5. DDBMS Disadvantages Complexity of management and control Security
Lack of standards
Increased storage requirements
Greater difficulty in managing data environment
Increased training costs
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

6. Distributed Processing
Shares database’s logical processing among physically, networked independent sites
Figure 10.1
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

7. Distributed Database
Stores logically related database over physically independent sites
Figure 10.2
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

8. Distributed Database vs. Distributed Processing
Does not require distributed database
May be based on a single database on single computer
Copies or parts of database processing functions must be distributed to all data storage sites
Distributed database
Requires distributed processing
Both
Require a network to connect components
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

9. Functions of DDBMS Application/end user interface
Validation to analyze data requests
Transformation to determine request components
Query optimization to find the best access strategy
Mapping to determine the data location
I/O interface to read or write data
Formatting to prepare the data for presentation
Security to provide data privacy
Backup and recovery
DB Administration
Concurrency Control
Transaction Management
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

10. Centralized Database Figure 10.3
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

11. Fully Distributed Database Management System
Figure 10.4
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

12. DDBMS Components Computer workstations
Network hardware and software components
Communications media
Transaction processor (TP)
Also called application manager (AP) or transaction manager (TM)
Data processor (DP)
Also called data manager (DM)
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

13. Distributed Database Components
Figure 10.5
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

14. DDBMS Protocols
Interface with network to transport data and commands between DPs and TPs
Synchronize data received from DPs and route to appropriate TPs
Ensure common database functions
Security
Concurrency control
Backup and recovery
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

15. Levels of Data and Process Distribution
Database systems can be classified based on process distribution and data distribution
Table 10.1
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

16. Single-Site Processing, Single-Site Data (SPSD)
All processing on single CPU or host computer
All data are stored on host computer disk
DBMS located on the host computer
DBMS accessed by dumb terminals
Typical of mainframe and minicomputer DBMSs
Typical of 1st generation of single-user microcomputer database
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel 22

17. Single-Site Processing, Single-Site Data (con’t.)
Figure 10.6
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel 22

18. Multiple-Site Processing, Single-Site Data (MPSD)
Requires network file server
Applications accessed through LAN
Variation known as client/server architecture
Figure 10.7
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel 24

19. Multiple-Site Processing, Multiple-Site Data (MPMD)
Fully distributed DDBMS with support for multiple DPs and TPs at multiple sites
Homogeneous I
Integrate one type of centralized DBMS over the network
Heterogeneous
Integrate different types of centralized DBMSs over a network
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel 26

20. Heterogeneous Distributed Database Scenario
Figure 10.8
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

21. Distributed DB Transparency
Allows end users to feel like only database user
Hides complexities of distributed database
Transparency features
Distribution
Transaction
Failure
Performance
Heterogeneity
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel 28

22. Distribution Transparency
Allows management of a physically dispersed database as though it were centralized
Three Levels
Fragmentation transparency
Location transparency
Local mapping transparency
Table 10.2
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

23. Transaction Transparency
Ensures transactions maintain integrity and consistency
Completed only if all involved database sites complete their part of the transaction
Management mechanisms
Remote request
Remote transaction
Distributed transaction
Distributed request
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

24. Remote Request
Figure 10.10
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

25. Remote Transaction Figure 10.11
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

26. Distributed Transaction
Figure 10.12
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

27. Distributed Requests Figure 10.13
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

28. Distributed Requests (con’t.)
Figure 10.14
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

29. Distributed Concurrency Control
Multisite, multiple-process operations more likely to create data inconsistencies and deadlocked transactions
Problems
Transaction committed by local DP
One DP could not commit transaction’s result
Yields inconsistent database
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

30. Two-Phase Commit Protocol
DO-UNDO-REDO protocol
Write-ahead protocol
Two kinds of nodes
Coordinator
Subordinates
Phases
Preparation
Coordinator sends message to all subordinates
Confirms all are ready to commit or abort
Final Commit
Ensures all subordinates have committed or aborted
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

31. Performance Transparency and Query Optimization
Objective: Minimize total cost associated with execution of request
Main costs
Access time
Communication
CPU time
Basis for query optimization algorithms
Optimum execution order
Sites accessed to minimize communication costs
Dynamic or static optimization
Statistically based vs. rule-based query optimization algorithms
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

32. Distributed Database Design
Partition database into fragments
Horizontal
Vertical
Mixed
Fragments to replicate
Storage of data copies at multiple sites
Fully, partially, unreplicated databases
Data allocation
Where to locate data
Centralized, partitioned, replicated
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

33. Client/Server Advantages Over DDBMS
Client/server less expensive
Client/server solutions allow use of microcomputer’s GUI
More people with PC skills than mainframe skills
PC is well established in workplace
Numerous data analysis and query tools exist
Considerable cost advantages to off-loading application development
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

34. Client/Server Disadvantages
Creates more complex environment with different platforms
Increased number of users and sites creates security problems
Training issues become more complex and expensive
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

35. Date’s 12 Commandments for Distributed Databases
1. Local Site Independence
2. Central Site Independence
3. Failure Independence
4. Location Transparency
5. Fragmentation Transparency
6. Replication Transparency
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel

36. Date’s 12 Commandments for Distributed Databases
7. Distributed Query Processing
8. Distributed Transaction Processing
9. Hardware Independence
10. Operating System Independence
11. Network Independence
12. Database Independence
Database Systems: Design, Implementation, & Management, 5th Edition, Rob & Coronel