Download Database Systems: Design, Implementation, and

Chapter
12
Distributed
Database
Management
Systems
Let us
ponder…..
“So what is a Distributed
Database…sounds like
a Disturbing Database!”
“So why would anyone
want to have a
Distributed Database,
anyway!”
So, how does it work –
this fancy DDB?”
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What is Distributed Database?
Wotz the difference?
Centralised Database vs Distributed Database
CDB v DDB
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So wotz the difference?
So then is there a difference between
“Distributed processing” and
“Distributed database”?
Distributed Processing vs DDB
• Shares database’s logical
processing among physically,
networked independent sites
• Stores logically related database
over physically independent sites
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Ja well no fine
So what have we got here with all this centralised, distributed
processing, distributed database……?
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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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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Single-Site Processing,
Single-Site Data
Figure 10.6
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Multiple-Site Processing,
Single-Site Data (MPSD)
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Multiple-Site Processing,
Single-Site Data (MPSD)
• Requires network file server
• Applications accessed through LAN
• Variation known as client/server architecture
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Multiple-Site Processing,
Multi Data (MPMD)
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Multiple-Site Processing,
Multiple-Site Data (MPMD)
• Fully distributed DDBMS with support
for sites
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Too easy
OK, so then the Database is at all the sites, the processing takes place at all
the sites….Ummm…
Do all the sites have the same type of database? Huh?
Homogeneous vs
Heterogeneous DDB
• Homogeneous
• Integrate one type of centralized DBMS over the network
• Heterogeneous
• Integrate different types of centralized DBMSs over a
network
No kidding……
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Heterogeneous Distributed
Database Scenario
Figure 10.8
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So why?
“So why would anyone want to have a Distributed Database,
anyway!”
DDBMS Advantages
• Two main reasons
• Speed
• Data located near site with greatest demand
• Multiple/Parallel processing
• Reliability
• Improved communications
• Redundant copies – no single point failure
Yeah…but surely
it’s not all roses
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DDBMS Disadvantages
• Two main thorns
• Complex
• Setup
• Management
• Security & Control
• Remote data
• Data communications
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So How?
So, how does it work – this fancy DDB?”
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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Distributed Database
Components
Figure 10.5
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The clever bit is….
The important part is what is invisible…..
Distributed DB Transparency
Distributed DB
Transparency
• Allows end users to feel like only
database user
• Hides complexities of distributed
database
• Transparency features
• Location
• Fragmentation
• Heterogeneity
• etc
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Distributed Transaction
Figure 10.12
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The hard bit…
is Concurrency Control
is Query Optimisation
is Integrity/Standards Control
is Security Controls
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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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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