private void addInputPaths(JobConf job, MergeFileWork work) {
    for (Path path : work.getInputPaths()) {
      FileInputFormat.addInputPath(job, path);
    }
  }
start a new map-reduce job to do the merge, almost the same as ExecDriver.
ql/src/java/org/apache/hadoop/hive/ql/io/merge/MergeFileTask.java