Universal Analytics: UserId, Session Unification and log out

Question

The documentation about Session Unification seems to state that when on, if the requests progress from not having userId to have an actual one, it considered the same user; but if the requests suddenly stop having the userId parameter, it is considered a log out and those request are not considered part of the same user.

Session Unification ON, see step 4:

So what would happen if a request with no userId is issued in between two with userId?

1. {clientId:1, userId:5}
2. {clientId:1}
3. {clientId:1, userId:5}

Does the lack of userId in request #2 causes a tear down of the user timeline in GA? Is request #3 accounted as part of the user?

Answer 1

In your example, the hits/events in Session #1 and #3 will be merged, but not from #2. Thus, userId 5 will show 2 sessions in the user-id view. In the 'all' view, you'll have 3 sessions and 1 user.