Oracle RAC and SCAN Listeners
I have a 4 node RAC architecture and SCAN Listeners are running on 3 nodes. As Oracle recommends minimum of 3 SCAN Listeners in the below blog.
http://satya-racdba.blogspot.in/2012/09/scan-in-oracle-rac-11g-r2.html
But is it necessary to configure SCAN on the 4th Listener as well?
Is the 4th Node being picked up by the SCAN listeners?
How do I test it?
Oracle does not reccomends miiumum of three scna listeners. Oracle states:
SCAN is a domain name registered to at least one and up to three IP addresses, either in the domain name service (DNS) or the Grid Naming Service (GNS).
You can find this information in Metalink Note:
Grid Infrastructure Single Client Access Name (SCAN) Explained (Doc ID 887522.1)
In the image you can see an exampel architecture of oracle SCAN:
A new set of cluster processes called scan listeners will run on three nodes in a cluster (or all nodes if there are less than 3). If you have more than three nodes, regardless of the number of nodes you have, there will be at most three scan listeners. The database registers with the SCAN listener through the remote listener parameter in the init.ora/spfile. If any of these clustered processes fail, they are automatically restarted on a new node.
If you have to do an installation you'd better to review the Oralce documentation: D Oracle Grid Infrastructure for a Cluster Installation Concepts
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