1. Distributed Database
Management Systems

2. Different Types of Database System
Contributed by:
Isha Kushwah
MCA-2008-11
Centralized database System
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3. Content
• What a distributed database management system
(DDBMS)
• DDBMS components
• 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
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4. Problem in Centralized database
Management
• Performance degradation
• High cost
• Reliability problems
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5. 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
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6. DDBMS Disadvantages
• Complexity of management and control
• Security
• Lack of standards
• Increased storage requirements
• Greater difficulty in managing data environment
• Increased training costs
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7. Distributed Processing
Shares database’s logical processing among
physically, networked independent sites
Figure 10.1
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8. Distributed Database
Stores logically related database over physically
independent sites
Figure 10.2
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9. Distributed Database
vs. Distributed Processing
• 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
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10. Functions of DDBMS
• Application/end user interface
• Validation
• Transformation
• Query optimization
• Mapping
• I/O interface
• Formatting
• Security
• Backup and recovery
• DB Administration
• Concurrency Control
• Transaction Management
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11. Centralized Database
Figure 10.3
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12. Fully Distributed Database
Management System
Figure 10.4 14

13. 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)
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14. Distributed Database Components
Figure 10.5
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15. 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
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16. Levels of Data and Process
Distribution
Database systems can be classified based on
process distribution and data distribution
Table 10.1
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17. 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
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18. Single-Site Processing, Single-Site
Data (con’t.)
Figure 10.6
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19. Multiple-Site Processing, Single-Site
Data (MPSD)
• Requires network file server
• Applications accessed through LAN
• Variation known as client/server architecture
Figure 10.7
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20. 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
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21. Heterogeneous Distributed Database
Scenario
Figure 10.8
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22. Distributed DB Transparency
• Allows end users to feel like only database user
• Hides complexities of distributed database
• Transparency features
– Distribution
– Transaction
– Failure
– Performance
– Heterogeneity
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23. 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
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24. 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
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25. Remote Request
Figure 10.10
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26. Remote Transaction
Figure 10.11
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27. Distributed Transaction
Figure 10.12
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28. Distributed Requests
Figure 10.13
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29. Distributed Requests (con’t.)
Figure 10.14
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30. 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
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31. 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
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32. 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
• Automatic or Manual
• Dynamic or static optimization
• Statistically based vs. rule-based query
optimization algorithms 34

33. 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
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34. 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
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35. 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
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36. 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
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37. 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
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