Server Roles in Replication

Servers can have three roles in SQL Server replication. All SQL Server 6.0 servers are capable of performing all of these roles.

• Publication server. A server that has made data available for replication. A publication server maintains publication databases, makes published data from those databases available for replication, and sends copies of all changes to the published data to the distribution server. Also referred to as a publisher.
• Distribution server. The server containing the distribution database. The distribution server receives all changes to published data, stores the changes in its distribution database, and, when appropriate (depending on scheduling and other variables), transmits them to subscription servers. The distribution server can be the same computer that is acting as the publication server, or a different computer. Also referred to as a distributor.
• Subscription server. A server that maintains destination databases, which receive and maintain copies of published data. Also referred to as a subscriber.

In most cases, the first two roles are combined in one computer; the publication server also acts as the distribution server, as shown in this illustration:

Note that the publishing and subscribing roles are not exclusive: servers can simultaneously perform both. For example, suppose Server A publishes Publication 1, and Server B publishes Publication 2. In this case, Server A could act both as a publication server (of Publication 1) and a subscription server (to Publication 2).

As an option, the distribution server can be installed on a separate computer, as shown in the following illustration. This might be an appropriate configuration when high loads are present, such as when a busy on-line transaction processing (OLTP) server is configured as a publication server. Using a separate distribution server reduces local processing and disk usage on the publication server, although it somewhat increases overall network traffic.

Note that using a separate distribution server requires separate SQL Server installations (two licenses), one for the publication server and one for the distribution server.