@Override
  public void map(Object key, Object value, OutputCollector output,
      Reporter reporter) throws IOException {

    row[0] = key;
    row[1] = value;
    try {
      mergeOp.process(row, 0);
    } catch (HiveException e) {
      abort = true;
      throw new IOException(e);
    }
  }
Mapper for fast file merging of ORC and RC files. This is very similar to
ExecMapper except that root operator is AbstractFileMergeOperator. This class
name is used for serialization and deserialization of MergeFileWork.
ql/src/java/org/apache/hadoop/hive/ql/io/merge/MergeFileMapper.java