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Oracle RAC and Replication Failover (KBA1240)


Q: How do SCANs works with RAC, especially if an instance dies? Is there automatic failover of the client?

Single Client Access Name (SCAN) is a new Oracle RAC 11g Release 2 feature that provides a single name for clients to access Oracle Databases running in a cluster. The benefit is that the client’s connect information does not need to change if they add or remove nodes in the cluster. The SCAN name typically resolves to multiple virtual IP addresses, with each virtual IP associated with a different node in a RAC cluster. If a single node in the cluster becomes unavailable, the SCAN will no longer resolve to the virtual IP of that failed node but rather will resolve to one of the available nodes. SCANs are NOT available for Oracle 10gR2 or 11gR1 RAC clusters.

Delphix supports the use of SCANs wherever available. For example, if the source database cluster is running in an 11gR2 environment, the JDBC string that Delphix uses to connect to the database will use the SCAN. When Delphix provisions a VDB into an 11gR2 cluster, the JDBC string we use to connect will be using the SCAN.

Q: How does Delphix handle failover in cases where SCANs are not available, such as 10gR2 and 11gR1 clusters? 

For source and target database environments running Oracle 10gR2 or 11gR1, Delphix will use virtual IP addresses instead of SCANs. Virtual IP addresses are more limited than SCANs because they are associated with specific nodes -- if a node associated with a virtual IP becomes unavailable the connection will fail after the TCP timeout (5 minutes). Delphix maintains a list of all the virtual IPs associated with a cluster, so if any one connection fails, it will simply round robin to the next virtual IP on the list after the previous connection times out. 

Q: Does Delphix have the notion of a primary node in a RAC Cluster?

Delphix does not have the notion of a primary instance. All nodes will be treated equally.

Q: Will virtual IPs be supported for non-RAC databases (e.g., ServiceGuard, Veritas Cluster Server)?

No. Virtual IPs are associated with Oracle clusters – these are Oracle virtual IPs, not general purpose IPs.