code: protected function getCacheKey($method, $fetchMode, $rawSql)
      {
          return [
              __CLASS__,
              $method,
              $fetchMode,
              $this->db->dsn,
              $this->db->username,
              $rawSql,
          ];
      }
docs: Returns the cache key for the query.
  
  @param string $method method of PDOStatement to be called
  @param int $fetchMode the result fetch mode. Please refer to [PHP manual](https://secure.php.net/manual/en/function.PDOStatement-setFetchMode.php)
  for valid fetch modes.
  @param string $rawSql the raw SQL with parameter values inserted into the corresponding placeholders
  @return array the cache key
  @since 2.0.16