The Microsoft® SQL Server™ version 7.0 replication model is based on the publish and subscribe metaphor popularized by SQL Server 6.0. The replication model consists of:
The Publisher is a server that makes data available for replication to other servers. In addition to identifying which data is to be replicated, the Publisher detects which data has changed and maintains information about all publications at that site. Any given data element that is replicated has a single Publisher, even if it may be updated by any number of Subscribers or published again by a Subscriber.
The Distributor is the server that contains the distribution database. The exact role of the Distributor is different in each type of SQL Server 7.0 replication.
Subscribers are servers that store replicas and receive updates. In earlier versions of SQL Server, updates could typically be performed only at the Publisher. However, SQL Server 7.0 allows Subscribers to make updates to data (but a Subscriber making updates is not the same as a Publisher). A Subscriber can, in turn, become a Publisher to other Subscribers.
A publication is a collection of articles, and an article is a grouping of data to be replicated. An article can be an entire table, only certain columns (using a vertical filter), only certain rows (using a horizontal filter), or even a stored procedure (in some types of replication). A publication often has multiple articles. This grouping of multiple articles makes it simpler to subscribe to a unit (the publication), which has all the relevant and required data. Subscribers subscribe only to a publication, not to individual articles within a publication.
With a push subscription, the Publisher propagates the changes to a Subscriber without a request from the Subscriber to do so. Typically, push subscriptions are used in applications that are required to send changes to Subscribers whenever and as soon as they occur. Push subscriptions are best for publications that require near-real-time movement of data without polling and where the higher processor overhead at the Publisher does not affect performance. Changes can also be pushed to Subscribers on a scheduled basis.
With a pull subscription, the Subscriber asks for periodic updates of all changes at the Publisher. Pull subscriptions are best for publications having a large number of Subscribers (for example, Subscribers using the Internet). Pull subscriptions are also best for autonomous mobile users because they allow the user to determine when the data changes are synchronized. A single publication can support a mixture of push and pull subscriptions.
The above replication components are implemented using a modular design. You can install these components on separate computers to balance workloads and minimize SQL Server replication’s effect on server performance.
| Configuring Replication | Subscribing to Publications |
| Publishing Data and Stored Procedures |