SQL Server 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. It is useful to divide replication into two broad categories: replicating data in a server to server environment and replicating data between a server and clients. Replicating data between servers typically supports improving scalability and availability, data warehousing and reporting, and integrating data from multiple sites. Replicating data between servers and clients typically supports exchanging data with mobile users, consumer point of sale (POS) applications, and integrating data from multiple sites.
Replication uses a publishing industry metaphor to represent the components in a replication topology, which include Publisher, Distributor, Subscribers, publications, articles, and subscriptions. Although the magazine metaphor is useful for understanding replication, it is important to note that SQL Server replication includes functionality that is not represented in this metaphor, particularly the ability for a Subscriber to make updates and for a Publisher to send out incremental changes to the articles in a publication.
There are three types of replication: transactional replication, merge replication, and snapshot replication. All of these types rely on a number of standalone programs, called agents, that carry out the tasks associated with tracking changes and distributing data.