code: def _wal_name(cls):
          
          if cls._WAL_NAME is None:
              version = cls._dict_transform(psql_csv_run(
                      "SELECT current_setting('server_version_num')"))
              if int(version['current_setting']) >= 100000:
                  cls._WAL_NAME = 'wal'
              else:
                  cls._WAL_NAME = 'xlog'
          return cls._WAL_NAME
docs: Sets and returns _WAL_NAME to 'wal' or 'xlog' depending on
          version of postgres we are working with.
  
          It is used for handling xlog -> wal rename in postgres v10