public Map<String, Long> getAllCountersInGroup(String groupName) {
    Map<String, Long> counterMap = _pubCounters.get(groupName);
    if (counterMap == null) {
      counterMap = new HashMap<String, Long>(1);
    }
    return counterMap;
  }
Tez Counter Data defining data structure.
app/com/linkedin/drelephant/tez/data/TezCounterData.java