public function setDirectives($directives)
    {
        parent::setDirectives($directives);
        $lifetime = $this->getLifetime(false);
        if ($lifetime > self::MAX_LIFETIME) {
            $this->_log(
                'redis backend has a limit of 30 days (' . self::MAX_LIFETIME
                . ' seconds) for the lifetime'
            );
        }
    }