In addition to data latency, site autonomy is an important criterion when formulating a replication strategy. Site Autonomy Correlates with Latency Site autonomy is the degree of independence between the source server and any secondary servers. Some forms of replication require a tight coupling between source and secondary systems. For instance, IUS requires the Publisher and updating Subscriber to be online simultaneously to complete the two-phase commit protocol. The Publisher is the server that makes data available to other servers participating in the replication activity.
Subscribers receive and apply the data updates provided by the Publisher through a Distributor.
Other replication methods can endure significant logical separation. With merge replication, a Subscriber can be entirely disconnected and miss one or more data updates, but receive the updates when it is back online. With snapshot replication, entire publications are sent over the wire at each replication cycle. Therefore, the next cycle will update disconnected Subscribers after they have rejoined the replication process. Note that data latency and site autonomy requirements and characteristics move in unison.