code: private String createReceivedAtKey(String fromClusterName,
  		String toClusterName) {
  
  		return KEY_PREFIX + fromClusterName + "-" + toClusterName
  			+ KEY_POSTFIX_DURATION;
  	}
docs: Creates the receivedAt key
  
  @param fromClusterName
  - the name of cluster from which the entry received
  @param toClusterName
  - the name of cluster on which the entry received
  @return - the receivedAt key