DISTRIBUTED DATABASES AND DDBMS. Learning Objectives Describe various DDBMS implementations ...
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DISTRIBUTED DATABASES AND DDBMS
Learning Objectives
Describe various DDBMS implementations
Explain how database design affects the DDBMS environment
Apply DDBMS principles to solve problems
Definitions
Distributed Database: A single logical database that is spread physically across computers in multiple locations that are connected by a data communications link
Decentralized Database: A collection of independent databases on non-networked computers
They are not the same thing!
Distributed database environments (adapted from Bell and Grimson, 1992)
Identical DBMSs
Homogeneous Database
Source: adapted from Bell and Grimson, 1992.
Typical Heterogeneous Environment
Non-identical DBMSs
Source: adapted from Bell and Grimson, 1992.
Example of Replication•Customers•Sales Staff
•Orders
CRM Db
•All Customers•All Sales Staff
•All Orders
N. America
•All Customers•All Sales Staff
•All Orders
Europe
User’s View of Db
Actual Implementation
Master Replica
Example of Horizontal Partitioning
•Customers•Sales Staff
•Orders
CRM Db
•NA Customers•NA Sales Staff
•NA Orders
N. America
•E Customers•E Sales Staff
•E Orders
Europe
User’s View of Db
Actual Implementation
Example of Vertical Partitioning
•Financials•Customer Service
•Prod. Support•Human Resources
ERP System
•Financials•Human Resources
N. America
•Customer Service•Prod Support
Europe
User’s View of Db
Actual Implementation
Five Distributed Database Organizations
Centralized database, distributed access Replication with periodic snapshot
update Replication with near real-time
synchronization of updates Partitioned, one logical database Partitioned, independent, nonintegrated
segments
Distributed Design Strategies
Distributed DBMS: Transparency Location Transparency
User/application does not need to know where data resides
Replication Transparency User/application does not need to know about
duplication Failure Transparency
Either all or none of the actions of a transaction are committed
Applying the concepts through examples: Client server: Mono, 2-tier, 3-tier, n-tier? Single Site / Multi Site data? Y/N
If multi-site: Partitioned H/V or Replicated? Location Transparency: Y/N? Replication Transparency: Y/N? Failure Transparency: Y/N?
Distributed DBMS architecture
Local Transaction Steps1. Application makes request to
distributed DBMS2. Distributed DBMS checks distributed
data repository for location of data. Finds that it is local
3. Distributed DBMS sends request to local DBMS
4. Local DBMS processes request5. Local DBMS sends results to application
Distributed DBMS Architecture - cont. Showing local transaction steps
Local transaction – all data stored locally
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Global Transaction Steps1. Application makes request to distributed DBMS2. Distributed DBMS checks distributed data
repository for location of data. Finds that it is remote
3. Distributed DBMS routes request to remote site4. Distributed DBMS at remote site translates request
for its local DBMS if necessary, and sends request to local DBMS
5. Local DBMS at remote site processes request6. Local DBMS at remote site sends results to
distributed DBMS at remote site7. Remote distributed DBMS sends results back to
originating site8. Distributed DBMS at originating site sends results
to application
Distributed DBMS architecture – contShowing global transaction steps
Global transaction – some data is at remote site(s)
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DISTRIBUTED DATABASE AND DDBMS
Questions?