void selectRawHostPartitionClassStorageStatsMap(
      Map<String, Map<Long, Map<Short, Map<Short, ContainerStorageStats>>>> selectedHostPartitionClassStorageStatsMap,
      Map<String, Map<Long, Map<Short, Map<Short, ContainerStorageStats>>>> hostPartitionClassStorageStatsMap,
      Map<Long, Long> partitionTimestampMap, Map<Long, Long> partitionPhysicalStorageMap, long snapshotTimestamp,
      String instanceName) {
    for (String partitionClassName : hostPartitionClassStorageStatsMap.keySet()) {
      if (!selectedHostPartitionClassStorageStatsMap.containsKey(partitionClassName)) {
        logger.trace("First entry for partitionClass {} is from {}", partitionClassName, instanceName);
        selectedHostPartitionClassStorageStatsMap.put(partitionClassName,
            hostPartitionClassStorageStatsMap.get(partitionClassName));
        // put all partitions associated with this partitionClass into partitionTimestampMap on their first occurrence.
        for (long partitionId : hostPartitionClassStorageStatsMap.get(partitionClassName).keySet()) {
          partitionTimestampMap.put(partitionId, snapshotTimestamp);
        }
      } else {
        selectRawHostAccountStorageStatsMap(selectedHostPartitionClassStorageStatsMap.get(partitionClassName),
            hostPartitionClassStorageStatsMap.get(partitionClassName), partitionTimestampMap,
            partitionPhysicalStorageMap, snapshotTimestamp, instanceName);
      }
    }
  }
Select the proper replica's partition class storage stats map the merge to the first map.
@param selectedHostPartitionClassStorageStatsMap The result map merged with proper replica's storage stats data.
@param hostPartitionClassStorageStatsMap Single host's partition class storage stats map.
@param partitionTimestampMap The map from partition id to the partition's snapshot timestamp.
@param partitionPhysicalStorageMap The map from partition id to the partition's physical storage usage.
@param snapshotTimestamp The snapshot timestamp for the given host.
@param instanceName The host's instance name.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/MySqlClusterAggregator.java