Bug #71312
Updated by Markus Klein about 4 years ago
on login the field 'is_online' is written with a timestamp.
on interaction with the site the field is updated.
so you can consider an user as inactive if the timestamp is older than N minutes.
but if an user explicit logs out the field is not cleared but the last value stays in the field.
in this way you can not decide active users, as the the logged out user may have been called pages up until the logout and got a newer timestamp than an user which is reading for some time on a page and may interact in the next minute as his login is still valid.