What is the advantage of using a rolling upgrade in an Oracle RAC environment?

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"A rolling patch refers to the cluster binaries being applied on databases of the RAC environment that are up and running. The advantage of this is that the patch can be applied to the cluster binaries without shutting down the database in a RAC environment. The cluster nodes are rolled one after another to compensate for the patched node being unavailable. All of the other instances are kept in an open state."