public static int partitionIdFromStatsPartitionKey(String partitionKey) {
    return Integer.valueOf(partitionKey.substring("Partition[".length(), partitionKey.length() - 1));
  }
Return partition id from partition key of stats report. It's the opposite of {@link #statsPartitionKey}.
@param partitionKey the partition key of stats report.
@return The partition id.
ambry-utils/src/main/java/com/github/ambry/utils/Utils.java