Primary and secondary database servers

When you configure a set of database servers to use data replication, one database server is called the primary database server, and the others are called secondary database servers. (In this context, a database server that does not use data replication is called a standard database server.) The secondary server can include any combination of the SD secondary, RS secondary, and HDR secondary servers.

As the following figure illustrates, the secondary database server is dynamically updated, with changes made to the data that the primary database server manages.
Figure 1: A primary and secondary database server in a data replication configuration

This figure is described in the surrounding text.
If one of the database servers fails, as the following figure shows, you can redirect the clients that use that database server to the other database server in the pair, which becomes the primary server.
Figure 2: Database servers and clients in a data replication configuration after a failure

This figure shows client computers redirected to the secondary database server after the primary database server fails.