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.