@Override
    public void writeKey(RandomAccessOutput dest) throws SerDeException {
      byte[] keyBytes = key.getBytes();
      int keyLength = key.getLength();
      dest.write(keyBytes, 0, keyLength);
    }
If we received data with tags from ReduceSinkOperators, no keys will match. This should
not happen, but is important enough that we want to find out and work around it if some
optimized change causes RSO to pass on tags.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/MapJoinBytesTableContainer.java