RE: Doubt Regarding Scan Listener

Just think of the SCAN address and the associated SCAN listeners as being a simplified way of managing connectivity to your cluster. When pushing out a TNS Names file on 10g or 11gR1 RAC, you would have to use the ADDRESS_LIST to specify the nodes associated with the cluster. This means that any time you add/remove nodes from the cluster, you're having to modify your TNSNames entry as well (which can sometimes be on hosts that you don't have access to). The SCAN simplifies this, one name for the cluster, resolves to 3 scan ip addresses, each related to a scan listener that will be running on some node in your cluster (where they run is not important, and will vary between reboots or cluster reconfigurations). When a client initiates a connection, one of the scan listeners picks it up (round robin) and will see what service the client is connecting to in the connection string. It will then do a handoff to the appropriate node in the cluster, and all future communication will be between the host and the client, the SCAN listener's work is done at that point.

This is a good summarization: http://www.oracle.com/technetwork/products/clustering/overview/scan-129069.pdf

Thanks,
Scott

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