A list of alternate database servers that is used to failover new or lost connections, depending on the failover method selected. See "Using failover" for information about choosing a failover method.
If using a tnsnames.ora file to retrieve connection information, do not specify this property. See "Using tnsnames.ora files" for more information.
The server name (servername1, servername2, and so on) is required for each alternate server entry. Port number (port1, port2, and so on) and connection properties (property=value) are optional for each alternate server entry. If the port is unspecified, the port number of the primary server is used. If the port number of the primary server is unspecified, the default port number of 1521 is used.
Optional connection properties are ServiceName and SID.
Notes
If using failover with an Oracle RAC, the primary server must be a primary node and any alternate server must be a secondary node.
Example
The following URL contains alternate server entries for server2 and server3. The alternate server entries contain the optional ServiceName property. Similarly, you can use the optional SID property instead.
If using failover with an Oracle RAC, the primary server must be a primary node and any alternate server must be a secondary node.