Publications and subscriptions v7

Replication Server uses an architecture called publish and subscribe. The data made available for copying by a replication system is defined as a publication. To get a copy of that data, you must "subscribe" to that publication. The manner in which you subscribe is slightly different for single-master and multi-master replication systems.

In Replication Server, a publication is defined as a named set of tables and views in a database. The database that contains the publication is called the publication database of that publication.

In a single-master replication system, to get a copy of a Replication Server publication, you must create a subscription. A Replication Server subscription is a named association of a publication to a database to which to copy the publication. This database is called the subscription database.

Similar to a single-master replication system, when creating a multi-master replication system, you first define a publication in the publication database. You then add one or more databases that you want to participate in this multi-master replication system. As you add each database, it is associated with this replication system. You don't create an explicit, named subscription in a multi-master replication system.

In a single-master replication system, replication occurs when Replication Server starts and completes either of the following processes:

• Applies changes that were made to rows in the publication since the last replication occurred to rows in tables of the subscription database (called synchronization).
• Copies rows of the publication to empty tables of the subscription database (called a snapshot). See Snapshot and synchronization overview.

The subscription tables are the tables in the subscription database created from corresponding tables or views in the publication.

In a multi-master replication system, the concept and definition of replication is nearly identical to a single-master replication system with the following modifications:

• Synchronization can occur between any pair of databases (referred to as primary nodes) participating in the replication system.
• A snapshot can occur from the publication database designated as the primary definition node to any of the other primary nodes.

The following diagram shows a multi-master replication system with three primary nodes.

This diagram shows that a table that was created as a member of a subscription can be used in a publication replicating to another subscription. This scenario is called cascading replication.

The following diagram shows a multi-master replication system with three primary nodes.