Confused about sessions

[eluser]gunzour[/eluser]
Hi everyone, I'm relatively new to CodeIgniter so please bear with me. I've been trying to make heads or tails of CI's session support and the documentation is leaving me confused. So I have several questions:

- If I use CI's session class and configure it to store sessions in a database table, does this replace storing the user data in a cookie? Or is it stored in both places? The user guide doesn't seem to answer this.

- Does anyone know if the Native_session library at http://codeigniter.com/wiki/Native_session/ is compatible with the current version of CI? (It appears to be for CI 1.5)

- Any support for (or plans to support) storing CI session data in memcached?

- If I want to, can I just ignore CI's session class and use native PHP sessions directly?

- If I did this (used native PHP sessions directly), where would be the best place for me to place session_start()? In the constructor of a controller? In a "header" view? In a hook?

Thanks for your help.