Ora-01555 even after proper undo settings

Question

Hi All,
OS : Linux
Oracle : 10.2.0.3.0
Last few weeks i am keep on facing 01555 error for some queries.
Please see my undo settings below
SQL> show parameter undo
NAME                                 TYPE                              VALUE
undo_management                      string                            AUTO
undo_retention                       integer                           1200
undo_tablespace                      string                            UNDOTBS1###############################################
SQL> declare
retention number ;
undo_ts_size number ;
   begin
   retention := DBMS_UNDO_ADV.REQUIRED_RETENTION ;
   undo_ts_size := DBMS_UNDO_ADV.REQUIRED_UNDO_SIZE(retention) ;
   dbms_output.put_line('Current retention ' || retention );
   dbms_output.put_line('Required tablespace size is ' || undo_ts_size);
end ;
Current retention 1100903
Required tablespace size is 198527
PL/SQL procedure successfully completed.####################################################
Tablespace Name                     Ext. Mgt.  Seg. Mgt. Tablespace Size (in MB)       Used (in MB)       Free (in MB) Pct. Used
UNDOTBS1                            LOCAL      MANUAL                     16,500              *1,708*             14,792        10###############################################################################
As its an oracle 10.2.0 version, i read that oracle will adjust retention period based on the long running quries & undo advisor is giving recommondation to set tablespace size to 198 G but i cannot understand why my undo tablespace is only 10% used when i am getting ora 01555 error ? mence there is no problem with retention as well as space then where is the problem ?
Also i checked if there is any stealing/reuse is happening but this below query returns 0
select UNXPSTEALCNT,UNXPBLKREUCNT from V$UNDOSTAT;
           0             0
           0             0
576 rows selected.
SQL>#########################################################
Could you please help me to identify the problem which i am facing ?
Thanks
Nisanth Santhan

Answer 1

but as per the below document, in 10.2 onwards even if we set undo retention, oracle will automatically adjust the retention based on the long running query . It seems we can even set 0 for undo retention. I have checked, my current auto undo retention setting is (1100822 sec).
http://www.oracle.com/technology/products/manageability/database/pdf/ow04/1241_minhas_pres.pdf