private function increment()
    {
        $query = $this->pdo->prepare(<<<SQL
INSERT INTO robotstxt__delay0 (base, userAgent, delayUntil, lastDelay)
VALUES (:base, :userAgent, (UNIX_TIMESTAMP(CURTIME(6)) + :delay) * 1000000, :delay * 1000000)
ON DUPLICATE KEY UPDATE
  delayUntil = GREATEST((UNIX_TIMESTAMP(CURTIME(6)) + :delay) * 1000000, delayUntil + (:delay * 1000000)),
  lastDelay = :delay * 1000000;
SQL
        );
        $query->bindValue('base', $this->base, \PDO::PARAM_STR);
        $query->bindValue('userAgent', $this->userAgent, \PDO::PARAM_STR);
        $query->bindValue('delay', $this->delay, \PDO::PARAM_INT);
        return $query->execute();
    }