DBMS:Centralised vs Distributed
|Table of contents|
Large commercial databases may exist in two different Topologies.
- Centralised - where the database is physically in one location and users typically use an Internet connection to access it. Banks (such as ANZ) tend to use centralised databases.
- Distributed - Where the database is in many locations often where you have a national or international company and customers tend to regularly interact with a local branch. For example: Google uses Big-Table a distributed DBMS as searching tends to be by users in a particular region of the world.
In both cases the database "looks" like one database.
Objective Data and database administrator
By the end of this page you will be able to:
- A single database maintained in one location.
- Managed by a database administrator. (usually )
- Access via a communications network
- Terminals provide distributed access
- Some major banks do all their processing on a mainframe, in some cases in a different country.
- Clients may use several branches, and online banking for transactions.
- Airline reservation systems need to be centralised to avoid double bookings.
- Inland Revenue in New Zealand is countrywide
- In NZ Police and ambulance calls are sent to a central call center.
|Question: For a National call centre (NZ Police/Ambulance) - What are potential Problems?|
- Increased reliability and availability
- Modular (incremental) growth
- Lower communication costs
- Faster Response
- Software cost and complexity
- Processing overheads
- Data integrity
A single logical database that is spread physically across computers in multiple locations that are connected by a data communications link.
- Most processing is local
- Need for local ownership of data
- Data sharing require
Note that users think they are working with a single corporate database
- Chain Stores like the MSD Spears (50% locally owned)
- Google: Use a DBMS called Bigtable. (Note it is not a Relational Database).("What database does Google use?", 2010; Chang,F., et al.,2006)
- Minimise communications
- Local control
- Adds to complexity and cost
- Processing overheads
- Data Integrity
- What database does Google use? (2010) In StackOverflow wiki. Retrieved September 19, 2010 from http://stackoverflow.com/questions/362956/what-database-does-google-use
- Chang,F., Dean, J., Ghemawat, S., Hsieh, WC., Wallach, D.A., Burrows,M., Chandra, T., Fikes, A., Gruber, R.E. (2006) Bigtable: A Distributed Storage System for Structured Data. Retrieved September 19, 2010 from http://labs.google.com/papers/bigtable-osdi06.pdf