Sessions

[eluser]pistolPete[/eluser]
Your explanation of the database use is correct, but the second one is not:
CI does not use native PHP sessions, so using only a cookie means that all of the data is put in the cookie instead of a serverside storage.

The use of the database is probably slower, but you could store more data than in the cookie.

Do you have to use sesssions at all for the search form? Isn't it possible to put the search terms in the URI?