void mergeAccountStorageStatsMap(Map<Short, Map<Short, ContainerStorageStats>> result,
      Map<Short, Map<Short, ContainerStorageStats>> current) {
    for (Map.Entry<Short, Map<Short, ContainerStorageStats>> currentEntry : current.entrySet()) {
      short accountId = currentEntry.getKey();
      if (!result.containsKey(accountId)) {
        result.put(accountId, currentEntry.getValue());
      } else {
        for (Map.Entry<Short, ContainerStorageStats> containerStorageStatsEntry : currentEntry.getValue().entrySet()) {
          short containerId = containerStorageStatsEntry.getKey();
          if (!result.get(accountId).containsKey(containerId)) {
            result.get(accountId).put(containerId, containerStorageStatsEntry.getValue());
          } else {
            ContainerStorageStats existingStats = result.get(accountId).get(containerId);
            ContainerStorageStats currentStats = containerStorageStatsEntry.getValue();
            ContainerStorageStats newStats = currentStats.add(existingStats);
            result.get(accountId).put(containerId, newStats);
          }
        }
      }
    }
  }
Merge two maps from account id to container id to storage stats. If the storage stats exists in both map, this method
will add the storage stats up and replace the existing storage stats in first map with the new one. If it only exists
in the second map, this method would add it to the first map.
@param result The resulting map
@param current The map to merge to the resulting map.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/MySqlClusterAggregator.java