@Override
    public void close() throws IOException {
      // ColumnizedDeleteEventRegistry reads all the delete events into memory during initialization
      // and it closes the delete event readers after it. If an exception gets thrown during
      // initialization, we may have to close any readers that are still left open.
      while (!sortMerger.isEmpty()) {
        Entry<DeleteRecordKey, DeleteReaderValue> entry = sortMerger.pollFirstEntry();
        entry.getValue().close(); // close the reader for this entry
      }
    }
@return how many delete events are actually loaded
ql/src/java/org/apache/hadoop/hive/ql/io/orc/VectorizedOrcAcidRowBatchReader.java