A distributed database is a database that is under the control of a central database management system (DBMS) in which storage devices are not all attached to a common cpu. It may be stored in multiple computers located in the same physical location, or may be dispersed over a network of interconnected computers.
Collections of data (eg. in a database) can be distributed across multiple physical locations. A distributed database is distributed into separate partitions/fragments. Each partition/fragment of a distributed database may be replicated .
Besides distributed database replication and fragmentation, there are many other distributed database design technologies. For example, local autonomy, synchronous and asynchronous distributed database technologies. These technologies' implementation can and does definitely depend on the needs of the business and the sensitivity/confidentiality of the data to be stored in the database, and hence the price the business is willing to spend on ensuring data security, consistency and integrity.
Advantages of Distributed Databases
1) Reflects organizational structure:- Database fragments are located in the departments they relate to.
2) Local autonomy:- A department can control the data about them (as they are the ones familiar with it.)
3) Improved availability:- A fault in one database system will only affect one fragment, instead of the entire database.
4) Improved performance:- Data is located near the site of greatest demand, and the database systems themselves are parallelized, allowing load on the databases to be balanced among servers. (A high load on one module of the database won't affect other modules of the database in a distributed database.)