private void setVarsInConf(int id) {

    // Following two config keys are required by FileOutputFormat to work
    // correctly.
    // In usual case of Hadoop, JobTracker will set these before launching
    // tasks.
    // Since there is no jobtracker here, we set it ourself.
    conf.setInt("mapred.task.partition", id);
    conf.set("mapred.task.id", "attempt__0000_r_000000_" + id);
  }
This writer writes via {@link HCatOutputFormat}
hcatalog/core/src/main/java/org/apache/hive/hcatalog/data/transfer/impl/HCatOutputFormatWriter.java