Replication Sites

A replication group can exist at multiple replication sites. Replication environments support two basic types of sites: master sites and materialized view sites. One site can be both a master site for one replication group and a materialized view site for a different replication group. However, one site cannot be both the master site and the materialized view site for the same replication group.

The differences between master sites and materialized view sites are the following:

• A replication group at a master site is more specifically referred to as a master group. A replication group at a materialized view site is based on a master group and is more specifically referred to as a materialized view group. Additionally, every master group has exactly one master definition site. A replication group's master definition site is a master site serving as the control center for managing the replication group and the objects in the group. If necessary, you can change the master definition site.

• A master site maintains a complete copy of all objects in a replication group, while materialized views at a materialized view site can contain all or a subset of the table data within a master group. For example, if the hr_repg master group contains the tables employees and departments, then all of the master sites participating in a master group must maintain a complete copy of employees and departments. However, one materialized view site might contain only a materialized view of the employees table, while another materialized view site might contain materialized views of both the employees and departments tables or a subset of these tables.

• All master sites in a multimaster replication environment communicate directly with one another to continually propagate data changes in the replication group. Materialized view sites contain an image, or materialized view, of the table data from a certain point in time. Typically, a materialized view is refreshed periodically to synchronize it with its master site. You can organize materialized views into refresh groups. Materialized views in a refresh group can belong to one or more materialized view groups, and they are refreshed at the same time to ensure that the data in all materialized views in the refresh group correspond to the same transactionally consistent point in time.