How to save changes in DB

I am having a shopping cart page which displays following information

Item No.,Description,Order Type,Quantity,available Qty,Dealer Information,Comments,Purchase Order Number

and some more fields(exactly 20). And at this point of time in cart I am having 20 sku.

I need to make this cart as persistent cart,

ie I have to save all changes made by user in following scenarios

1. If user changes anything I have to save it in db.

2. After adding item to cart, user logout.

3. User changes and goes to different page.

4. User changes qty and gone to take bath.

So How to do it, according to me possible solutions are

1.For all the events use AJAX to save the particular field. (But gives performance issue)

2. Save the value of changed element in session and save it in db when user navigates or logout

Thanks in Advacne!!