Long term history of sessions : what would be the unique key ?

Hello all,

i want to evaluate the history of longer running sessions. I created an enrichted copy of v$active_session_history and i am looking for a logical primary key . I presume sid + serial + thread  together don't suffice.  I did not find , under which circumstances these values are recycled, but I am quite sure they are. AWR , ASH and friends are organized by time (snapshots) but I am interested in the 'biography' of some longer running sessions during their lifetime., which is sometimes days unfortunately..

Hmmmm. I hope this is somewaht clear ....

Thanks for listening

Norbert