ClientProtocol getStats Method and its Application

ClientProtocol.getStats() return 7 types of statistics information.

 /**
   * Get a set of statistics about the filesystem.
   * Right now, only seven values are returned.
   * <ul>
   * <li> [0] contains the total storage capacity of the system, in bytes.</li>
   * <li> [1] contains the total used space of the system, in bytes.</li>
   * <li> [2] contains the available storage of the system, in bytes.</li>
   * <li> [3] contains number of under replicated blocks in the system.</li>
   * <li> [4] contains number of blocks with a corrupt replica. </li>
   * <li> [5] contains number of blocks without any good replicas left. </li>
   * <li> [6] contains number of blocks which have replication factor
   *          1 and have lost the only replica. </li>
   * </ul>
   * Use public constants like {@link #GET_STATS_CAPACITY_IDX} in place of 
   * actual numbers to index into the array.
   */
  @Idempotent
  public long[] getStats() throws IOException;

DFSClient.callGetStats is client side interface

 private long[] callGetStats() throws IOException {
    checkOpen();
    TraceScope scope = Trace.startSpan("getStats", traceSampler);
    try {
      return namenode.getStats();
    } finally {
      scope.close();
    }
  }

DFSClient separates the statistics use different methods.

/**
   * @see ClientProtocol#getStats()
   */
  public FsStatus getDiskStatus() throws IOException {
    long rawNums[] = callGetStats();
    return new FsStatus(rawNums[0], rawNums[1], rawNums[2]);
  }

  /**
   * Returns count of blocks with no good replicas left. Normally should be 
   * zero.
   * @throws IOException
   */ 
  public long getMissingBlocksCount() throws IOException {
    return callGetStats()[ClientProtocol.GET_STATS_MISSING_BLOCKS_IDX];
  }

  /**
   * Returns count of blocks with replication factor 1 and have
   * lost the only replica.
   * @throws IOException
   */
  public long getMissingReplOneBlocksCount() throws IOException {
    return callGetStats()[ClientProtocol.
        GET_STATS_MISSING_REPL_ONE_BLOCKS_IDX];
  }

  /**
   * Returns count of blocks with one of more replica missing.
   * @throws IOException
   */ 
  public long getUnderReplicatedBlocksCount() throws IOException {
    return callGetStats()[ClientProtocol.GET_STATS_UNDER_REPLICATED_IDX];
  }

  /**
   * Returns count of blocks with at least one replica marked corrupt. 
   * @throws IOException
   */ 
  public long getCorruptBlocksCount() throws IOException {
    return callGetStats()[ClientProtocol.GET_STATS_CORRUPT_BLOCKS_IDX];
  }