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Replication is the continuous copying of data changes from one database (publisher) to another database (subscriber). The two databases are generally located on a different physical servers, resulting in a load balancing framework by distributing assorted database queries and providing failover capability. The server for the subscriber database may be configured as a backup in the event of failure of the server for the publisher database.
Techopedia Explains Replication
When implementing replication, database systems use a variety of methods but use the same concept. If there is a way to frequently copy data from one database to a second, or even to a third version of the same database, two main database administration goals may be achieved: failover capability and load balancing.
After data is distributed between two or more servers, querying users are not required to connect to a primary database. If replication is set up designating the primary database as the publisher, some queries can be redirected to the subscriber. Known as load balancing, this process is useful for databases that have high user traffic.
Replication can also provided failover capability. When data is held on two separate servers, a subscriber can be set up as the default primary if the publisher becomes unavailable.
There are three different replication methods:
- Snapshot Replication: Data is copied from the publisher to the subscribers.
Note: Subscriber changes must come from the publisher. Thus, only the subscriber may be queried; but its data cannot be edited by users. - Merge Replication: Data is combined from two or more databases into one super master database, which is trickier to implement than snapshot replication.
- Transactional Replication: The full database is copied, followed by publisher updates which are periodically copied to the subscriber(s).
If important data is accidentally deleted from the publisher, replication deletes the same data from its subscriber(s). Replication is not a substitute for backups.
