@Override
  public void close() throws IOException {
    super.close();
    // free the memory for the column vectors
    if (batch != null) {
      batch.cols = null;
    }
  }
If the current batch is empty, get a new one.
@return true if we have rows available.
@throws IOException
ql/src/java/org/apache/hadoop/hive/ql/io/orc/RecordReaderImpl.java