Flashback query on the v$transaction

Question

hi All,
if i know the SCN just before the transaction commit, after the transaction is commit, I can use flashback query on the v$transaction to get the info about the transaction, such as undo segment number, used undo block.
Here comes the testcase, i use dbms_lock.sleep(6) because the smon_scn_time is updated every 6 seconds(Note ID: 281510.1)
the problem is that the flashback query on the v$transaction doest not work, no rows return at the last line.
any advice?
sys@SID10G> select * from v$version;
BANNER
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Prod
PL/SQL Release 10.2.0.4.0 - Production
CORE     10.2.0.4.0     Production
TNS for MacOS X Server: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
sys@SID10G> drop table t purge;
Table dropped.
sys@SID10G>
sys@SID10G> create table t as select * from all_objects where rownum <= 1000;
Table created.
sys@SID10G>
sys@SID10G> exec dbms_lock.sleep(6);
PL/SQL procedure successfully completed.
sys@SID10G>
sys@SID10G> update t set object_name = lower(object_name);
1000 rows updated.
sys@SID10G>
sys@SID10G> --save the current scn for later flashback query
sys@SID10G> col scn new_value _scn
sys@SID10G>
sys@SID10G> select dbms_flashback.get_system_change_number scn from dual;
       SCN
   6397848
sys@SID10G>
sys@SID10G> select xidusn, xidslot, xidsqn, used_ublk from v$transaction;
    XIDUSN    XIDSLOT     XIDSQN  USED_UBLK
         8         12       4725          8
sys@SID10G>
sys@SID10G> select dbms_flashback.get_system_change_number scn from dual;
       SCN
   6397848
sys@SID10G>
sys@SID10G> commit;
Commit complete.
sys@SID10G>
sys@SID10G> exec dbms_lock.sleep(6);
PL/SQL procedure successfully completed.
sys@SID10G> select xidusn, xidslot, xidsqn, used_ublk from v$transaction as of scn &_scn;
old   1: select xidusn, xidslot, xidsqn, used_ublk from v$transaction as of scn &_scn
new   1: select xidusn, xidslot, xidsqn, used_ublk from v$transaction as of scn    6397848
no rows selectedEdited by: Sidney Chen on Aug 7, 2011 3:33 PM

Answer 1

Please see,
http://download.oracle.com/docs/cd/E11882_01/appdev.112/e17125/adfns_flashback.htm#g1703502
You cannot retrieve past data from a dynamic performance (V$) view. A query on such a view always returns current data.Aman....