protected function handle_error($query)
    {
        $error = $this->dbh->errorInfo();

        // retry after "Deadlock found when trying to get lock" errors
        $retries = 2;
        while ($error[1] == 1213 && $retries >= 0) {
            usleep(50000);  // wait 50 ms
            $result = $this->dbh->query($query);
            if ($result !== false) {
                return $result;
            }
            $error = $this->dbh->errorInfo();
            $retries--;
        }

        return parent::handle_error($query);
    }