code: public SimpleJob setBigJoin(String[] masterLabels, String masterColumn, String dataColumn,
                                  String masterPath, String separator) {
          if (natural) {
              throw new RuntimeException("Not supported big join for natural job.");
          }
  
          bigJoin = true;
          conf.setInt(READER_TYPE, SINGLE_COLUMN_JOIN_READER);
          conf.setStrings(MASTER_LABELS, masterLabels);
          conf.set(JOIN_MASTER_COLUMN, masterColumn);
          conf.set(JOIN_DATA_COLUMN, dataColumn);
          conf.set(MASTER_PATH, masterPath);
          conf.set(MASTER_SEPARATOR, separator);
          return this;
      }
docs: to join the data that does not fit into memory.
  @param masterLabels label of master data
  @param masterColumn master column
  @param dataColumn data column
  @param masterPath master data HDFS path
  @param separator separator
  @return this