How to identify unique visitors

[sangoku]

Hy i`m making a site which needs to identify unique users so far nothing new.

 

Now because i want to identify the visitors as unique ones    i am thinking to give each of them a  cookie with a random generated value in it and i plan to note their ip address to.

 

now i am thinking of making a table in which i store following values

 

IP, cookie value, visiting time

 

My question is are there any better options to identify the unique visitors than this... which would mean  less load on my DB >?<

 

Because this solution would load my BD pretty hard Q.Q

 

And i dont want to take any chance with it, mean i want 99,99% secure way to identify unique users.... any suggestions on this????