Wednesday, April 17, 2013

IP Addresses and Oracle RAC

There are 3 types of IP addresses used in RAC:

  • Private IP - used for internal communication between the cluster nodes
  • Public IP - regular IP address used to communicate with the network
  • Virtual IP - used by database applications to enable failover when one node fails

Connections to the server are done through listener, and if connection has been established and listener fails, that's not an issue since after connection has been established, there is no need for a listener. Now if the net connection is trying to get a session while listener os down, the user will get an error message as connection fails. That's in a regular environment.

In RAC environment database is in a sharing mode - shared between all conencted nodes thus more than 1 listener is running in various nodes. So if a listener is down and user process is trying to get a connection, RAC will automatically transfer that request to another listener on a different node.

Before physical IP addresses were used in listener configuration which is a disadvantage over using virtual IP addresses because when using physical IP the session will wait for a timeout before failing over to another node. using Virtual IP (VIP) in listener coniguration because Oracle Notifiction Service (OBS) maintains the communication between the nodes and will notify all the nodes and listeners whenever one of the nodes is down, and VIP of the failed node will automatically divert to surviving node and session will be established in that node. There won't be any wait for TCP/IP timeout event.

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