Database replication is the frequent electronic copying data from a database in one computer or server to a database in another so that all users share the same level of information. The result is a distributed database in which users can access data relevant to their tasks without interfering with the work of others. The implementation of database replication for the purpose of eliminating data ambiguity or inconsistency among users is known as normalization.
Database replication can be done in at least three different ways:
- Snapshot replication: Data on one server is simply copied to another server, or to another database on the same server.
- Merging replication: Data from two or more databases is combined into a single database.
- Transactional replication: Users receive full initial copies of the database and then receive periodic updates as data changes.
A distributed database management system (DDBMS) ensures that changes, additions, and deletions performed on the data at any given location are automatically reflected in the data stored at all the other locations. Therefore, every user always sees data that is consistent with the data seen by all the other users.