In RAC if any node becomes inactive, or if other nodes are unable to ping/connect to a node in the RAC, then the node which first detects that one of the node is not accessible, it will evict that node from the RAC group. e.g. there are 4 nodes in a rac instance, and node 3 becomes unavailable, and node 1 tries to connect to node 3 and finds it not responding, then node 1 will evict node 3 out of the RAC groups and will leave only Node1, Node2 & Node4 in the RAC group to continue functioning.
The split brain concepts can become more complicated in large RAC setups. For example there are 10 RAC nodes in a cluster. And say 4 nodes are not able to communicate with the other 6. So there are 2 groups formed in this 10 node RAC cluster ( one group of 4 nodes and other of 6 nodes). Now the nodes will quickly try to affirm their membership by locking controlfile, then the node that lock the controlfile will try to check the votes of the other nodes. The group with the most number of active nodes gets the preference and the others are evicted.
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