DBMS:Centralised vs Distributed

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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.


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Objective Data and database administrator

By the end of this page you will be able to:

  • Describe the features, advantages and disadvantages of:
    • Distributed Database, and
    • Centralised

Centralised

ANZ: Banking online
  • A single database maintained in one location.
  • Managed by a database administrator. (usually )
  • Access via a communications network
    • LAN
    • WAN
    • Terminals provide distributed access

Examples

  • 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.

Advantages

  • Increased reliability and availability
  • Modular (incremental) growth
  • Lower communication costs
  • Faster Response

Disadvantages

  • Software cost and complexity
  • Processing overheads
  • Data integrity

Distributed database

Google search: Pacman at http//www.google.com/pacman

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

Examples

  • 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[1]; Chang,F., et al.,2006[2])

Advantages

  • Minimise communications
  • Costs
  • Local control

Disadvantages

  • Adds to complexity and cost
  • Processing overheads
  • Data Integrity

Review

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Review questions

  1. Distinguish between a distributed and centralized database when would you each of these?
  2. Describe two features of a Centralised database, and give an example.
  3. Describe two features of a Distributed database, and give an example.
  4. List advantages and disadvantages of a Centralised Database
  5. List advantages and disadvantages of a Distributed Database

Icon References.png References

  1. What database does Google use? (2010) In StackOverflow wiki. Retrieved September 19, 2010 from http://stackoverflow.com/questions/362956/what-database-does-google-use
  2. 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

DBMS:Centralised vs Distributed. (2017). In virtualMV's ( Michael Verhaart ) wiki. Retrieved December 17, 2017, from http://www.virtualmv.com/wiki/index.php?title=DBMS%3ACentralised_vs_Distributed    (zotero)