public InputSplit getSplit(int idx) {
    assert (idx >= 0 && idx < inputSplits.length);
    return inputSplits[idx];
  }
HiveInputSplit encapsulates an InputSplit with its corresponding
inputFormatClass. The reason that it derives from FileSplit is to make sure
"map.input.file" in MapTask.
ql/src/java/org/apache/hadoop/hive/ql/io/BucketizedHiveInputSplit.java