Cannot unserialize ci_sessions from database

In CI 3.0 it doe's not look like they are using the unserialize and serialize methods anymore.

Best to look at the session class to see what's going on.

I try to looking CI_Session_database_driver.php, and I found Serialized session data
But I still don't understand  
I've poor skill of PHP

PHP Code:

/**
     * Read
     *
     * Reads session data and acquires a lock
     *
     * @param    string    $session_id    Session ID
     * @return    string    Serialized session data
     */
    public function read($session_id)
    {
        if ($this->_get_lock($session_id) !== FALSE)
        {
            // Needed by write() to detect session_regenerate_id() calls
            $this->_session_id = $session_id;

            $this->_db
                ->select('data')
                ->from($this->_config['save_path'])
                ->where('id', $session_id);

            if ($this->_config['match_ip'])
            {
                $this->_db->where('ip_address', $_SERVER['REMOTE_ADDR']);
            }

            if (($result = $this->_db->get()->row()) === NULL)
            {
                $this->_fingerprint = md5('');
                return '';
            }

            // PostgreSQL's variant of a BLOB datatype is Bytea, which is a
            // PITA to work with, so we use base64-encoded data in a TEXT
            // field instead.
            $result = ($this->_platform === 'postgre')
                ? base64_decode(rtrim($result->data))
                : $result->data;

            $this->_fingerprint = md5($result);
            $this->_row_exists = TRUE;
            return $result;
        }

        $this->_fingerprint = md5('');
        return '';
    }

    // ------------------------------------------------------------------------

    /**
     * Write
     *
     * Writes (create / update) session data
     *
     * @param    string    $session_id    Session ID
     * @param    string    $session_data    Serialized session data
     * @return    bool
     */
    public function write($session_id, $session_data)
    {
        // Was the ID regenerated?
        if ($session_id !== $this->_session_id)
        {
            if ( ! $this->_release_lock() OR ! $this->_get_lock($session_id))
            {
                return FALSE;
            }

            $this->_row_exists = FALSE;
            $this->_session_id = $session_id;
        }
        elseif ($this->_lock === FALSE)
        {
            return FALSE;
        }

        if ($this->_row_exists === FALSE)
        {
            $insert_data = array(
                'id' => $session_id,
                'ip_address' => $_SERVER['REMOTE_ADDR'],
                'timestamp' => time(),
                'data' => ($this->_platform === 'postgre' ? base64_encode($session_data) : $session_data)
            );

            if ($this->_db->insert($this->_config['save_path'], $insert_data))
            {
                $this->_fingerprint = md5($session_data);
                return $this->_row_exists = TRUE;
            }

            return FALSE;
        }

        $this->_db->where('id', $session_id);
        if ($this->_config['match_ip'])
        {
            $this->_db->where('ip_address', $_SERVER['REMOTE_ADDR']);
        }

        $update_data = array('timestamp' => time());
        if ($this->_fingerprint !== md5($session_data))
        {
            $update_data['data'] = ($this->_platform === 'postgre')
                ? base64_encode($session_data)
                : $session_data;
        }

        if ($this->_db->update($this->_config['save_path'], $update_data))
        {
            $this->_fingerprint = md5($session_data);
            return TRUE;
        }

        return FALSE;
    }

    // ------------------------------------------------------------------------