docs: def _get_pid_file_variable(self, db):
          """
          Get the `pid_file` variable
          """
          pid_file = None
          try:
              with closing(db.cursor()) as cursor:
                  cursor.execute("SHOW VARIABLES LIKE 'pid_file'")
                  pid_file = cursor.fetchone()[1]
          except Exception:
              self.warning("Error while fetching pid_file variable of MySQL.")
  
          return pid_file