Tengo una tabla con sesiones en línea como esta (las filas vacías son solo para una mejor visibilidad):

ip_address  | start_time       | stop_time
------------|------------------|------------------
10.10.10.10 | 2016-04-02 08:00 | 2016-04-02 08:12
10.10.10.10 | 2016-04-02 08:11 | 2016-04-02 08:20

10.10.10.10 | 2016-04-02 09:00 | 2016-04-02 09:10
10.10.10.10 | 2016-04-02 09:05 | 2016-04-02 09:08
10.10.10.10 | 2016-04-02 09:05 | 2016-04-02 09:11
10.10.10.10 | 2016-04-02 09:02 | 2016-04-02 09:15
10.10.10.10 | 2016-04-02 09:10 | 2016-04-02 09:12

10.66.44.22 | 2016-04-02 08:05 | 2016-04-02 08:07
10.66.44.22 | 2016-04-02 08:03 | 2016-04-02 08:11

Y necesito el lapso de tiempo en línea "envolvente":

ip_address  | full_start_time  | full_stop_time
------------|------------------|------------------
10.10.10.10 | 2016-04-02 08:00 | 2016-04-02 08:20
10.10.10.10 | 2016-04-02 09:00 | 2016-04-02 09:15
10.66.44.22 | 2016-04-02 08:03 | 2016-04-02 08:11

Tengo esta consulta que devuelve el resultado deseado:

WITH t AS 
    -- Determine full time-range of each IP
    (SELECT ip_address, MIN(start_time) AS min_start_time, MAX(stop_time) AS max_stop_time FROM IP_SESSIONS GROUP BY ip_address),
t2 AS
    -- compose ticks
    (SELECT DISTINCT ip_address, min_start_time + (LEVEL-1) * INTERVAL '1' MINUTE AS ts
    FROM t
    CONNECT BY min_start_time + (LEVEL-1) * INTERVAL '1' MINUTE <= max_stop_time),
t3 AS 
    -- get all "online" ticks
    (SELECT DISTINCT ip_address, ts
    FROM t2
        JOIN IP_SESSIONS USING (ip_address)
    WHERE ts BETWEEN start_time AND stop_time),
t4 AS
    (SELECT ip_address, ts,
        LAG(ts) OVER (PARTITION BY ip_address ORDER BY ts) AS previous_ts
    FROM t3),
t5 AS 
    (SELECT ip_address, ts, 
        SUM(DECODE(previous_ts,NULL,1,0 + (CASE WHEN previous_ts + INTERVAL '1' MINUTE <> ts THEN 1 ELSE 0 END))) 
            OVER (PARTITION BY ip_address ORDER BY ts ROWS UNBOUNDED PRECEDING) session_no
    FROM t4)
SELECT ip_address, MIN(ts) AS full_start_time, MAX(ts) AS full_stop_time
FROM t5
GROUP BY ip_address, session_no
ORDER BY 1,2;

Sin embargo, estoy preocupado por el rendimiento. La tabla tiene cientos de millones de filas y la resolución de tiempo es milisegundos (no un minuto como se muestra en el ejemplo). Por lo tanto, CTEt3 va a ser enorme ¿Alguien tiene una solución que evite la autounión y "CONECTAR POR"?

Un solo inteligenteFunción analítica sería genial.