estimates given by views like undostats

Hi Guys,

Please share best approaches for Undo tablespace(monitoring and avoiding ORA-01555
like dyanamically monitoring undo usage(script,sql) and if possible alerting if reaching threshold
also with latest version can snap shot too old be prevented by init parameters

like if large batch job is running which can take many days to finish,how to ensure undo tablespace not reached it max value and impact failing of batch job
(apart from increasing undo size and retention),how reliable are estimates given by views like undostats for required size of undo table space

Thanks

CREATE OR REPLACE PROCEDURE stpgview_proc (p_array_size IN PLS_INTEGER DEFAULT 1000)
IS
TYPE ARRAY IS TABLE OF STATS_PAGE_DAILY%ROWTYPE;
l_data ARRAY;

CURSOR c IS SELECT * FROM STATS_PAGE_DAILY where log_date is not null;

BEGIN
    OPEN c;
    LOOP
    FETCH c BULK COLLECT INTO l_data LIMIT p_array_size;

    FORALL i IN 1..l_data.COUNT
    INSERT INTO STATS_PAGE_DAILY1 VALUES l_data(i);

    EXIT WHEN c%NOTFOUND;
    END LOOP;
    CLOSE c;
END stpgview_proc;

I have a batch job execute loading many rows from large table into clone one, I wrote PL/SQL, bulk collect

CREATE OR REPLACE PROCEDURE stpgview_proc (p_array_size IN PLS_INTEGER DEFAULT 1000)
IS
TYPE ARRAY IS TABLE OF STATS_PAGE_DAILY%ROWTYPE;
l_data ARRAY;

CURSOR c IS SELECT * FROM STATS_PAGE_DAILY where log_date is not null;

BEGIN
    OPEN c;
    LOOP
    FETCH c BULK COLLECT INTO l_data LIMIT p_array_size;

    FORALL i IN 1..l_data.COUNT
    INSERT INTO STATS_PAGE_DAILY1 VALUES l_data(i);

    EXIT WHEN c%NOTFOUND;
    END LOOP;
    CLOSE c;
END stpgview_proc;

INSERT INTO stats_page_daily1 
SELECT * 
FROM   stats_page_daily 
WHERE  log_date IS NOT NULL;