compatibility site - session and unique user id tie in with paypal

BACKGROUND:
im working on a couple compatibility website based on astrology. the workflow of the website is as below
1. user lands on local website
2. user enters his and partners birth details like date place time of birth (data not stored in database)
3. local website sends this data to a third party vendor which calculates the astrological charts and sends it back (data stored in mysql - multiple rows and columns - one big chunk, no unique identifier sent by vendor)
4. local website performs calculations and spits out a result
5. user pays through paypal
6. local website displays the result.

now the status is that paypal is working, and compatibility score is coming out fine

ISSUE:

i want the session to be set and unique id to be set so that each user is uniquely traceable and one user doesnt end up getting results mixed up with another user.

How do i go about doing this? step by step instruction will be very much appreciated.

By using CodeIgniter's session library.

You can find it in the CodeIgniter's User Guide.

What did you Try? What did you Get? What did you Expect?

Joined CodeIgniter Community 2009.  ( Skype: insitfx )

By using CodeIgniter's session library.

You can find it in the CodeIgniter's User Guide.

do i need to use unique id or is session enough?