code: private boolean register(String name, Metric metric)
      { 
          boolean ret = allColumnFamilyMetrics.putIfAbsent(name,  new HashSet<Metric>()) == null;
          allColumnFamilyMetrics.get(name).add(metric);
          all.add(name);
          return ret;
      }
docs: Registers a metric to be removed when unloading CF.
  @return true if first time metric with that name has been registered