public static MapJoinKey readFromRow(Output output, MapJoinKey key, Object[] keyObject,
      List<ObjectInspector> keyFieldsOI, boolean mayReuseKey) throws HiveException {
    MapJoinKeyObject result = mayReuseKey ? (MapJoinKeyObject)key : new MapJoinKeyObject();
    result.readFromRow(keyObject, keyFieldsOI);
    return result;
  }
Serializes row to output for vectorized path.
@param byteStream Output to reuse. Can be null, in that case a new one would be created.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/MapJoinKey.java