Republisher
The republisher model uses two servers to publish the same data. The Publisher sends data to a Subscriber, which then republishes the data to any number of Subscribers. This is useful when a Publisher must send data to Subscribers over a slow or expensive communications link. If there are a number of Subscribers on the far side of that link, using a republisher shifts the bulk of the distribution load to that side of the link.
In this diagram, both the Publisher and the republisher (publishing Subscriber) are acting as their own local Distributors. If each were set up to use a remote Distributor, each Distributor would need to be on the same side of the slow or expensive communications link as its Publisher. Publishers must be connected to remote Distributors by reliable, high-speed communications links.
Any server can act as both Publisher and Subscriber. For example, consider the publication of a table that exists in New York and needs to be distributed to four different cities in Europe: London, Oslo, Paris, and Lisbon. The server in London is chosen to subscribe to the published table originating in New York, because the London site meets these conditions:
- The network link back to New York is relatively reliable.
- The New York-to-London communication costs are acceptable.
- There are good network communications lines from London to all other European Subscriber sites.
