Shrink the history of updates for
        a `index/doc_type` combination down to `self.marker_index_hist_size`.

def ensure_hist_size(self):
        """
        Shrink the history of updates for
        a `index/doc_type` combination down to `self.marker_index_hist_size`.
        """
        if self.marker_index_hist_size == 0:
            return
        result = self.es.search(index=self.marker_index,
                                doc_type=self.marker_doc_type,
                                body={'query': {
                                    'term': {'target_index': self.index}}},
                                sort=('date:desc',))

        for i, hit in enumerate(result.get('hits').get('hits'), start=1):
            if i > self.marker_index_hist_size:
                marker_document_id = hit.get('_id')
                self.es.delete(id=marker_document_id, index=self.marker_index,
                               doc_type=self.marker_doc_type)
        self.es.indices.flush(index=self.marker_index)