@Override
  public AggregatedPartitionClassStorageStats queryAggregatedPartitionClassStorageStats() throws Exception {
    return aggregatedPartitionClassStats;
  }
Constructor to instantiate an {@link InmemoryAccountStatsStore}.
@param clusterName the clusterName
@param hostname the hostname
ambry-mysql/src/main/java/com/github/ambry/accountstats/InmemoryAccountStatsStore.java