code: def ensure_hist_size(self):
          
          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)
docs: Shrink the history of updates for
          a `index/doc_type` combination down to `self.marker_index_hist_size`.