static String getSargColumnIDsString(Configuration conf) {
    return conf.getBoolean(ColumnProjectionUtils.READ_ALL_COLUMNS, true) ? null
        : conf.get(ColumnProjectionUtils.READ_COLUMN_IDS_CONF_STR);
  }
Take the configuration and figure out which columns we need to include.
@param readerSchema the types for the reader
@param conf the configuration
ql/src/java/org/apache/hadoop/hive/ql/io/orc/OrcInputFormat.java