docs: public void updateCount(String lastPrefix, int diff) {
          String statNode = Quotas.statPath(lastPrefix);
          DataNode node = nodes.get(statNode);
          StatsTrack updatedStat = null;
          if (node == null) {
              // should not happen
              LOG.error("Missing count node for stat " + statNode);
              return;
          }
          synchronized (node) {
              updatedStat = new StatsTrack(new String(node.data));
              updatedStat.setCount(updatedStat.getCount() + diff);
              node.data = updatedStat.toString().getBytes();
          }
          // now check if the counts match the quota
          String quotaNode = Quotas.quotaPath(lastPrefix);
          node = nodes.get(quotaNode);
          StatsTrack thisStats = null;
          if (node == null) {
              // should not happen
              LOG.error("Missing count node for quota " + quotaNode);
              return;
          }
          synchronized (node) {
              thisStats = new StatsTrack(new String(node.data));
          }
          if (thisStats.getCount() < updatedStat.getCount()) {
              LOG
                      .warn("Quota exceeded: " + lastPrefix + " count="
                              + updatedStat.getCount() + " limit="
                              + thisStats.getCount());
          }
      }