session in db user_aget why not md5 mix?

[eluser]whatisnewone[/eluser]

Code:

user_agent varchar(120) NOT NULL,

VS

Code:

user_agent varchar(32) NOT NULL,

and

Code:

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/30.0.1599.101 Safari/537.36

VS

Code:

098e63faa10aff94683e8871ca54271d

sess_cookie_name length 420 VS 300

need user_aget ? use

Code:

$this->input->user_agent()

vs

Code:

$this->session->userdata('user_agent')

Better! right?