static String getNeededColumnNamesString(Configuration conf) {
    String orcSchemaOverrideString = conf.get(ColumnProjectionUtils.ORC_SCHEMA_STRING);

    if (orcSchemaOverrideString != null) {
      final String columnNameDelimiter = conf.get(serdeConstants.COLUMN_NAME_DELIMITER,
          String.valueOf(SerDeUtils.COMMA));
      return String.join(columnNameDelimiter, TypeDescription.fromString(orcSchemaOverrideString).getFieldNames());
    } else {
      return conf.get(ColumnProjectionUtils.READ_COLUMN_NAMES_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