code: def execute_query(self, tmaster, query_string, start, end):
      
      if not tmaster:
        raise Exception("No tmaster found")
      self.tmaster = tmaster
      root = self.parse_query_string(query_string)
      metrics = yield root.execute(self.tracker, self.tmaster, start, end)
      raise tornado.gen.Return(metrics)
docs: execute query