/**
   * Optimization hook. Override this to make SequenceFile.Sorter's scream.
   *
   * <p>The default implementation reads the data into two {@link WritableComparable}s (using {@link
   * Writable#readFields(DataInput)}, then calls {@link
   * #compare(WritableComparable,WritableComparable)}.
   */
  public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) {
    try {
      buffer.reset(b1, s1, l1); // parse key1
      key1.readFields(buffer);

      buffer.reset(b2, s2, l2); // parse key2
      key2.readFields(buffer);

    } catch (IOException e) {
      throw new RuntimeException(e);
    }

    return compare(key1, key2); // compare them
  }
 /**
  * Compare two WritableComparables.
  *
  * <p>The default implementation uses the natural ordering, calling {@link
  * Comparable#compareTo(Object)}.
  */
 @SuppressWarnings("unchecked")
 public int compare(WritableComparable a, WritableComparable b) {
   return a.compareTo(b);
 }