1. Distributed Database Management Systems

2. Reading
Textbook: Ch. 1, Ch. 3
For next class: Ch. 4
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3. Database Management System (DBMS)
Collection of
interrelated data and
set of programs to access the data
Convenient and efficient processing of data
Database Application Software
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4. Abstraction View level: different perspectives
application programs hide irrelevant data
Logical level: data models
Logical representation of data
Different approaches: relational, hierarchical, network, object oriented, semi-structured, etc.
Data independence principle
Physical level: how data is stored
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5. Motivation for DBMS Integrate related data
Provide centralized and controlled access to data
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6. Computer Network Distributed processing:
Number of autonomous processing elements that are interconnected by computer network
Cooperate to perform their assigned tasks
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7. What to distribute? Processing logic/element Functions Data
Control of execution
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8. Why to distribute?
Intuition
Reliability
Performance
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9. Distributed Database Systems
Collection of multiple, logically interrelated databases that are distributed over a computer network
Distributed DBMS: software system that
Permits the management of the distributed database and
Makes the distribution transparent to the user
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10. Data Delivery Data storage and query processing Data delivery:
Delivery mode: push, pull, hybrid
Frequency: periodic, conditional, ad-hoc, irregular
Communication method: unicast, one-to-many
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11. DDBMS Services Transparent data management Reliable access to data
Distributed, replicated data
Transparency: network, replica, fragmentation
Reliable access to data
Distributed transactions
Failure atomicity
Improved performance
Flexible expansion
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12. Difficulties Everything that is present in traditional DBs
Fragmentation and replica control
Data retrieval
Data update
Dealing with failures
Synchronization
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13. DDBMS Issues Database design Directory management Query processing
Concurrency control
Deadlock management
Reliability
Replication
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14. DDBMS Architecture Chapter 1.7 (read only) Client/server P2P
Multi-database
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15. Distributed Database Design
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16. Design Issues Placing of data and programs (DBMS and application)
Network issues
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17. Level of Sharing Heterogeneous environment! No sharing Data sharing
Data and program sharing
Heterogeneous environment!
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18. Access Pattern
Static
Dynamic
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19. Level of Knowledge on Access Behavior
Complete information
Partial information
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20. Top-Down Design
Figure 3.2
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21. Fragmentation Why to fragment the data? Application views
Limit replication while increase availability
Increased concurrency
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22. Fragmentation Types: Degree: Horizontal Vertical Hybrid
From no fragmentation to individual tuples/attributes
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23. Correctness of Fragmentation
Completeness: FR={R1, …, Rn}
Reconstruction: R=Ri, RiR
Disjointness:
Horizontal: does not  djRi such that djRk where ki
Vertical: same as horizontal for non-primary key attributes
1&2: Lossless-join (normalization)
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24. Allocation Replication or single copy? Issues: (Figure 3.6)
Read-only transactions
Issues: (Figure 3.6)
Query processing
Directory management
Concurrency control
Reliability
Real world applications
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25. Fragmentation Design Information need: Database information
Application information
Communication network information
Computer system information
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26. Horizontal Fragmentation
Primary horizontal fragmentation: defined by selection operation on the relations of a database schema, Ri= Fi(R)
Correctness:
Completeness
Reconstruction (union)
Disjointness
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27. Vertical Fragmentation
R={R1, …, Rn}, where each Ri (i=1, …, n) contains a primary key and some of the attributes in R
More difficult than horizontal fragmentation – heuristics
Grouping
Splitting
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28. Vertical Fragmentation
Correctness:
Completeness
Reconstruction (join)
Disjointness
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29. Hybrid Fragmentation
Horizontal or vertical fragmentations are not sufficient the user application requirements
Nested or mixed fragmentation
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30. Data Directory Global vs. local conceptual schemas How to search?
Where to store?
Single vs. multiple copies?
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31. Current Research Allocation: new requirements, technology, etc.
Where to store the fragments?
Dynamic environment
Usage pattern
Application characteristics
Network changes
Security
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32. Next Class
Commit Protocols
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