@Override
    public void set(RecordIdentifier other) {
      super.set(other);
      currentWriteId = ((ReaderKey) other).currentWriteId;
      isDeleteEvent = ((ReaderKey) other).isDeleteEvent;
    }
A RecordIdentifier extended with the current write id. This is the
key of our merge sort with the originalWriteId, bucket, and rowId
ascending and the currentWriteId, statementId descending. This means that if the
reader is collapsing events to just the last update, just the first
instance of each record is required.
ql/src/java/org/apache/hadoop/hive/ql/io/orc/OrcRawRecordMerger.java