code: public Set<String> getNodeSessions(String nodeName) {
      ClusterNode node = nameToNode.get(nodeName);
      if (node == null) {
        LOG.warn("Trying to get the sessions for a non-existent node " +
          nodeName);
        return new HashSet<String>();
      }
      synchronized (node) {
        return new HashSet<String>(hostsToSessions.get(node));
      }
    }
docs: Get all the sessions that have grants on the node
  @param nodeName the name of the node
  @return the set of session ids that are running on the node