When LeaseRenewer gets an IOException while attempting to renew for a client, it retries after sleeping 500ms. If the exception is caused by a condition that will never change, it keeps talking to the name node until the DFSClient object is closed or aborted. With the FileSystem cache, a DFSClient can stay alive for very long time. We've seen the cases in which node managers and long living jobs flooding name node with this type of calls.
The current proposal is to abort the client when RemoteException is caught during renewal. LeaseRenewer already does abort on all clients when it sees a SocketTimeoutException.