Mark this update as complete.

        The document id would be sufficent but,
        for documentation,
        we index the parameters `update_id`, `target_index`, `target_doc_type` and `date` as well.

def touch(self):
        """
        Mark this update as complete.

        The document id would be sufficent but,
        for documentation,
        we index the parameters `update_id`, `target_index`, `target_doc_type` and `date` as well.
        """
        self.create_marker_index()
        self.es.index(index=self.marker_index, doc_type=self.marker_doc_type,
                      id=self.marker_index_document_id(), body={
                          'update_id': self.update_id,
                          'target_index': self.index,
                          'target_doc_type': self.doc_type,
                          'date': datetime.datetime.now()})
        self.es.indices.flush(index=self.marker_index)
        self.ensure_hist_size()