Consider the following codes I collect from the libs/login.php file of Kahuk CMS:

    function SetIDCookie($what, $remember) {
        global $db;
        $domain = preg_replace('/^www/','',$_SERVER['HTTP_HOST']);
        // Remove port information.
        $port = strpos($domain, ':');
        if ($port !== false)  $domain = substr($domain, 0, $port);          
        if (!strstr($domain,'.') || strpos($domain,'localhost:')===0) $domain='';
        switch ($what) {
            case 0: // Borra cookie, logout
                setcookie ("mnm_user", "", time()-3600, "/",$domain); // Expiring cookie
                setcookie ("mnm_key", "", time()-3600, "/",$domain); // Expiring cookie
                setcookie ("mnm_data", "", time()-3600, "/",$domain); // Expiring cookie
                setcookie ("mnm_user", "", time()-3600, "/"); // Expiring cookie
                setcookie ("mnm_key", "", time()-3600, "/"); // Expiring cookie
                setcookie ("mnm_data", "", time()-3600, "/"); // Expiring cookie
                break;
            case 1: //Usuario logeado, actualiza el cookie
                // Atencion, cambiar aqu�cuando se cambie el password de base de datos a MD5
                $strCookie=base64_encode(join(':',
                    array(
                        $this->user_login,
                        crypt($this->user_login, 22),
                        $this->md5_pass)
                    )
                );
                if($remember){
                    $time = time() + (60 * 60 * 24 * 10); //Cookie will expire in 10 days if remember option is selected at login. 86400 = 1 day
                } else {
                    $time = 0; //Cookie will expire when browser session ends. Note: This may depend on your browser settings. Example: in Chrome if 'Continue where you left off' option is checked the cookie won't expire.
                }

                // Setting httponly and secure true to add additional security for cookies
                if(isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on') {
                    setcookie('mnm_user', $this->user_login, $time, '/',$domain, TRUE, TRUE);
                    setcookie('mnm_key', $strCookie, $time, '/',$domain, TRUE, TRUE);
                    setcookie('mnm_data', md5(sha1($this->ip.':'.$this->user_agent)), $time, '/', $domain, TRUE, TRUE);
                } else {
                    setcookie('mnm_user', $this->user_login, $time, '/',$domain, FALSE, TRUE);
                    setcookie('mnm_key', $strCookie, $time, '/',$domain, FALSE, TRUE);
                    setcookie('mnm_data', md5(sha1($this->ip.':'.$this->user_agent)), $time, '/', $domain, FALSE, TRUE);
                }

                break;
        }
    }

Whenever a new user logged-in in my website, it creates temporary cookies files for 10 days. Now my vps contain nearly a million temporary cookies files which makes the server almost down because the CPU takes too much time to find out correct cookies whenever get a new request.

What is the solutions?

Update:
JFYI, here is the session files and the content in a session file from my VPS server.