What is difference between distriduted database and centrlized database system?

Answer

This relates to deployment of application.

Centralized DB : Where the data for application shall be stored in one location and the users can access the database using the application provided from anywhere using the network (LAN/WAN/Internet etc)

Distributed DB: The application & the database shall be deployed where ever required and there will be some mechanism to synchronize the data between these databases.

In more of layman' s words:

In centralized DB the database is stored in a central server and all user have access to that DB, and any changes made by any user in DB is reflected in central DB, thus visible to all the users using it.

In distributed DB the DB is stored in multiple locations(say different computers on a lan or on a remote location comp). It is more of a kind of more than one copy of a single DB and changes in one copy doesn't reflects immediately , it is rather responsibility of DBA to ensure security and more importantly ensure the Integrity of Data in several locations(all copies).

Distrubuted DB is fast to work with but incurs a lot of head-ache for DBA to ensure Security and data Integrity, also expensive to maintain.

Whereas centralized DB is more reliable and reflects changes immediately thus ensuring data integrity and bit of less overhead in security. But Load on a centralized system is too high if users are more, so might slow down the performance and would incur greater response time.

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