@Override
  public boolean isDelete(OrcStruct value) {
    return OrcRecordUpdater.getOperation(value) == OrcRecordUpdater.DELETE_OPERATION;
  }
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