Flashback table not responding

Question

hi,
i am using oracle 10g R2 on linux X86. i have flashback feature set to true. one of my table was accidently truncated.
now i want it back.other tables are brought back with flashback technology.
but this one is generating error that "the table definition has been changed" i dont made any changes to table definition.
what might be the issue? even though i have backup,but still would like to know,and recover it with the help of flashback.
flashback retention target has been set to 900. and table was droped much before that.
plz help
thanks and regards
VD

Answer 1

Vikrant,
Why would I mind explaining?
Anyways, see below a small code.
SQL> create table aman_t (a number);
Table created.
SQL> desc dba_extents;
Name                                      Null?    Type
OWNER                                              VARCHAR2(30)
SEGMENT_NAME                                       VARCHAR2(81)
PARTITION_NAME                                     VARCHAR2(30)
SEGMENT_TYPE                                       VARCHAR2(18)
TABLESPACE_NAME                                    VARCHAR2(30)
EXTENT_ID                                          NUMBER
FILE_ID                                            NUMBER
BLOCK_ID                                           NUMBER
BYTES                                              NUMBER
BLOCKS                                             NUMBER
RELATIVE_FNO                                       NUMBER
SQL> select segment_name,extent_id,blocks from dba_extents where segment_name='AMAN_T';
SEGMENT_NAME
EXTENT_ID     BLOCKS
AMAN_T
         0          8
SQL> begin
  2  for i in 1..10000 loop
  3  insert into aman_t values(i);
  4  end loop;
  5  commit;
  6  end;
  7  /
PL/SQL procedure successfully completed.
SQL> select segment_name,extent_id,blocks from dba_extents where segment_name='AMAN_T';
SEGMENT_NAME
EXTENT_ID     BLOCKS
AMAN_T
         0          8
AMAN_T
         1          8
AMAN_T
         2          8
SQL> commit;
Commit complete.
SQL> exec dbms_stats.gather_table_stats(user,'AMAN_T');
PL/SQL procedure successfully completed.
SQL> select segment_name,extent_id,blocks from dba_extents where segment_name='AMAN_T';
SEGMENT_NAME
EXTENT_ID     BLOCKS
AMAN_T
         0          8
AMAN_T
         1          8
AMAN_T
         2          8
SQL> delete from aman_t;
10000 rows deleted.
SQL> exec dbms_stats.gather_table_stats(user,'AMAN_T');
PL/SQL procedure successfully completed.
SQL> select segment_name,extent_id,blocks from dba_extents where segment_name='AMAN_T';
SEGMENT_NAME
EXTENT_ID     BLOCKS
AMAN_T
         0          8
AMAN_T
         1          8
AMAN_T
         2          8
SQL> truncate table aman_t;
Table truncated.
SQL> exec dbms_stats.gather_table_stats(user,'AMAN_T');
PL/SQL procedure successfully completed.
SQL> select segment_name,extent_id,blocks from dba_extents where segment_name='AMAN_T';
SEGMENT_NAME
EXTENT_ID     BLOCKS
AMAN_T
         0          8
SQL>You should be able to see that when I issued a delete command, the number of allocated extents are the same.Which does mean that though the blocks are empty but the HWM is still pointing towards those blocks.I gathered stats just to ensure that you won't come back and say that aafter gathering them,things would be different.
When I gave truncate, you can see that oracle came back to the initially allocated first extent only. This is table definition change and this did happen with my last demo and with your original scenerio as well.
Now just to confuse you a little more, even gathering of stats would be called as definition change. See below,
SQL> drop table aman_t purge;
Table dropped.
SQL> create table amna_t( a char);
Table created.
SQL> exec dbms_stats.gather_table_stats(user,'AMNA_T');
PL/SQL procedure successfully completed.
SQL> alter table amna_t enable row movement;
Table altered.
SQL> flashback table amna_T to timestamp(sysdate - 1/24/60);
flashback table amna_T to timestamp(sysdate - 1/24/60)
ERROR at line 1:
ORA-01466: unable to read data - table definition has changed
SQL>So I hope you should be clear now that you can't get back the data with Flashback as this relies over the Undo data and can only get back the logical changes , not the structural changes over the object.
HTH
Aman....