What Is Merge Replication?

Consider the two of you as buddies. Let's call her Maria, the one buddy who never fails to share the most recent and delicious news and tidbits. The other pal, who we'll name Jake, is the one who maintains tabs on everything that goes on in the group. Although Maria and Jake are both highly competent in their fields, they have decided to share information frequently to ensure everything is clear. This is analogous to the process of Merge Replication, in which two databases share information and maintain consistency through mutual updates. Merge Replication is a specific kind of replication that facilitates the creation of several autonomous databases that share the same data. These databases can be in separate places and maintained by different people, but they all sync up to ensure everyone gets the same information. The term "synchronization" refers to sharing data between databases. Let's pretend for a moment that Jake is concerned that Maria has been out of the loop for a few weeks due to her travels. Maria's database is updated with the new information he sends her. This is functionally analogous to how Merge Replication works. If one database is behind on updates, the other can send the missing changes, and the lagging database can quickly become up-to-date. Here's the scientific bit: the Merge Replication setup consists of a Publisher, a Subscriber, and a Distributor. Simply put, the Publisher is the data repository eager to share its wealth of knowledge with the world. An interested database, or "Subscriber," is the entity that contacts a publisher to request content publication. The Distributor acts as a liaison between the Publisher and the Subscriber, facilitating communication between the two parties and ensuring they are in sync. Snapshot replication is the mechanism through which the Publisher and the Subscriber share data. Here, the Publisher transfers the full database to the Subscriber, and the latter adjusts its data to precisely mirror the Publishers. Repeatedly doing this ensures that all data is consistent between the two sources. In this context, the Distributor is a key player. It monitors the Publisher's database for updates and notifies the Subscriber of any changes. The Subscriber then makes the corresponding adjustments to its own database so that it also accurately reflects the information in the Publisher's database. Merge Replication is like having a long-distance friendship in which you and your friend routinely share updates so that you always have the most up-to-date information. In this analogy, the Publisher represents Maria, who has all the most up-to-date information, and the Subscriber, Jake, keeps meticulous records of everything. And the Distributor represents the go-between who facilitates the interchange of information and keeps everyone in sync. Even more so than in a personal relationship, Merge Replication success depends on open communication and trust.