@Override
  public void close() throws IOException {
    if (primary != null) {
      primary.getRecordReader().close();
    }
    for(ReaderPair pair: readers.values()) {
      pair.getRecordReader().close();
    }
  }
This determines the set of {@link ReaderPairAcid} to create for a given delta/.
For unbucketed tables {@code bucket} can be thought of as a write tranche.
ql/src/java/org/apache/hadoop/hive/ql/io/orc/OrcRawRecordMerger.java