Sessions logging

session_log: {
    total_sessions: 123456, //total number of sessions
    total_seconds: 42342, //total seconds in sessions
    total_days: 100, //total elapsed days (maybe not the best approach. this is to compute daily active users/sessions)
    sessions_by_month: {
        '2017-02': {
            groups: {
                group_id: 123 //sessions count of users in this group,
                other_group_id: 123 //sessions count of users in this group
            },
            sessions: {
                user_id: 123 //sessions count of this users,
                other_user_id: 123 //sessions count of this users
            }
        },
        '2017-03': {
            //...
        }
    },
    sessions_by_day: {
        '2017-02-19': {
            groups: {
                group_id: 123 //sessions count of users in this group,
                other_group_id: 123 //sessions count of users in this group
            },
            sessions: {
                user_id: 123 //sessions count of this users,
                other_user_id: 123 //sessions count of this users
            }
        },
        '2017-02-20': {
            //...
        }
    },
    sessions_by_hour: {
        '2017-02-19-00': {
            groups: {
                group_id: 123 //sessions count of users in this group,
                other_group_id: 123 //sessions count of users in this group
            },
            sessions: {
                user_id: 123 //sessions count of this users,
                other_user_id: 123 //sessions count of this users
            }
        },
        '2017-02-19-01': {
            //...
        }
    }
}