Replication is a set of technologies for copying and distributing data and database objects from one database to another and then synchronizing between databases to maintain consistency.

Types of Replication

In SQL Server three types of replication

1.    Snapshot Replication

This process is commonly used to provide the initial set of data and database objects for transactional and merge publications, but it can also be used by itself. It supports the following points.

·  Data changes infrequently.
·  It is acceptable to have copies of data that are out of date with respect to the Publisher for a period of time. 

2.    Transactional Replication

This Process is typically used in server-to-server environments and is appropriate in each of the following cases:

·   The application requires low latency between the time changes are made at the Publisher and the changes arrive at the Subscriber.
·    The application requires access to intermediate data states. For example - firing a trigger
·    The Publisher has a very high volume of insert, update, and delete activity.
·    Subscribers to transactional publication should be treated as read-only

3.    Merge Replication

This Process is typically used in server-to-client environments. Merge replication is appropriate in any of the following situations:
·    Multiple Subscribers might update the same data at various times and propagate those changes to the Publisher and to other Subscribers.
·    Subscribers need to receive data, make changes offline, and later synchronize changes with the Publisher and other Subscribers.
·    Each Subscriber requires a different partition of data.