Distributed Databases
By Adya Kastwar , SE EXTC
A distributed database is a database in which all the storage devices are not attached to a common processor . Parts of the data are stored in multiple physical locations and processing is distributed among multiple database nodes . The data on several computers can be simultaneously accessed and modified using a network . A distributed database system is different from a parallel system , which include strongly coupled processors that constitute a single database system . On the other hand , distributed database systems include weakly couple sites that do not have common physical components .
A centralized distributed database management system integrates the data logically so as to provide the same ease of management of data as experienced by all data saved in the same location . It periodically synchronizes all the data to ensure that all updates and deletions performed on the data at one location will be automatically reflected in the data stored elsewhere . Since Distributed databases store data at multiple sites , they may improve performance at the last worksites by allowing transactions to be processed on many machines , instead of one . Distributed databases can be accessed through : Local applications , which do not require data from other sites . Global applications , which require data from other sites .
Distributed databases can be homogenous or heterogeneous . In a homogeneous distributed database system , all the physical locations have the same underlying hardware and identical software and work together in processing user requests . Each site relinquishes a part of its freedom in the right to change software individually . A homogeneous DBMS acts as a single system as far as the user is concerned . It is is much easier to design and manage . In a heterogeneous distributed database , the hardware , operating systems or database applications may be different at each of the locations .