code: def search(self, start_ts, end_ts):
          
          for meta_collection_name in self._meta_collections():
              meta_coll = self.meta_database[meta_collection_name]
              for ts_ns_doc in meta_coll.find(
                  {"_ts": {"$lte": end_ts, "$gte": start_ts}}
              ):
                  yield ts_ns_doc
docs: Called to query Mongo for documents in a time range.