docs: def read_metadata(self, symbol, as_of=None, allow_secondary=None):
          """
          Return the metadata saved for a symbol.  This method is fast as it doesn't
          actually load the data.
  
          Parameters
          ----------
          symbol : `str`
              symbol name for the item
          as_of : `str` or int or `datetime.datetime`
              Return the data as it was as_of the point in time.
              `int` : specific version number
              `str` : snapshot name which contains the version
              `datetime.datetime` : the version of the data that existed as_of the requested point in time
          allow_secondary : `bool` or `None`
              Override the default behavior for allowing reads from secondary members of a cluster:
              `None` : use the settings from the top-level `Arctic` object used to query this version store.
              `True` : allow reads from secondary members
              `False` : only allow reads from primary members
          """
          _version = self._read_metadata(symbol, as_of=as_of, read_preference=self._read_preference(allow_secondary))
          return VersionedItem(symbol=symbol, library=self._arctic_lib.get_name(), version=_version['version'],
                               metadata=_version.pop('metadata', None), data=None,
                               host=self._arctic_lib.arctic.mongo_host)