Single-Master (Primary-to-secondary) Replication v6.2
xDB Replication Server performs primary-to-secondary replication when a single-master replication system is implemented. The publication is the master and the subscription is the secondary. In a primary-to-secondary relationship, changes are propagated in one direction only, from the master to the secondary.
Figure 2-6: Single-Master (Primary-to-secondary) replication
Generally, changes must not be made to the definitions of the publication tables or the subscription tables. If such changes are made to the publication tables, they are not propagated to the subscription and vice versa unless the DDL change replication feature is used as described in Replicating DDL Changes. If changes are made to the table definitions without using the DDL change replication feature, there is a risk that future replication attempts may fail.
Changes must not be made to the rows of the subscription tables. If such changes are made, they are not propagated back to the publication. If changes are made to the subscription table rows, it is fairly likely that the rows will no longer match their publication counterparts. There is also a risk that future replication attempts may fail.