"Oracle" uses bbed to recover delete data

The data in the table does not actually delete the data after it has been deleted, but instead it hits a delete tag that can be recovered only if it has not been overwritten.

The experimental steps are as follows:

[Email protected]>create table bbed_test (x varchar2 (20));

Table created.

[email protected]>insert into bbed_test values (' BADLY9 ');

1 row created.

[email protected]>insert into bbed_test values (' JP ');

1 row created.

[Email protected]>commit;

Commit complete.

[Email Protected]>select rowid, dbms_rowid.rowid_relative_fno (ROWID) Rel_fno,

2 Dbms_rowid.rowid_block_number (ROWID) Blockno,

3 Dbms_rowid.rowid_row_number (ROWID) rowno

4 from Bbed_test;

ROWID rel_fno Blockno ROWNO

------------------ ---------- ---------- ----------

AAAM0VAABAAAOUCAAA 1 60290 0

Aaam0vaabaaaoucaab 1 60290 1

[Email protected]>alter system flush Buffer_cache;

System altered.

[Email protected]>alter system dump datafile 1 block 60290;

System altered.

[Email Protected]>oradebug setmypid

Statement processed.

[Email Protected]>oradebug tracefile_name

/u01/app/oracle/admin/orcl/udump/orcl_ora_18509.trc

View dump file

Block_row_dump:

tab 0, row 0, @0x1f96

Tl:10 FB:--h-fl-- lb:0x1 cc:1

Col 0: [6] 4c 59 39

tab 0, row 1, @0x1f90

Tl:6 FB:--h-fl-- lb:0x1 cc:1

Col 0: [2] 4a 50

End_of_block_dump

The location of the red Marker records the status of the row's data :

If it is not deleted, it is --H-FL--, Its corresponding value is 0x2c

has been deleted is --hdfl--, its corresponding value is 0x3c

Let's take a look at the following line of data:

[Email protected]>delete bbed_test where x= ' BADLY9 ';

1 row deleted.

[Email protected]>commit;

Commit complete.

[Email Protected]>select * from Bbed_test;

X

--------------------

Jp

[Email protected]> alter system flush Buffer_cache;

System altered.

[Email protected]>alter system dump datafile 1 block 60290;

System altered.

View dump file

Block_row_dump:

tab 0, row 0, @0x1f96

Tl:2 FB:--hdfl-- lb:0x2

tab 0, row 1, @0x1f90

Tl:6 FB:--h-fl-- lb:0x0 cc:1

Col 0: [2] 4a 50

End_of_block_dump

You can see that the data for row 0 is now marked for deletion.

The following uses the bbed tool to restore the data back:

Bbed> Set DBA 1,60290

DBA 0x0040eb82 (4254594 1,60290)

Bbed> f/c BADLY9

File:/u01/app/oracle/oradata/orcl/system01.dbf (1)

block:60290 offsets:8182 to 8191 dba:0x0040eb82

------------------------------------------------------------------------

4241444c 59390206 1e62

<32 bytes per line>

Bbed> P *KDBR

ROWDATA[6]

----------

Ub1 Rowdata[6] @8178 0x3c

Bbed> Set Offset 8178

OFFSET 8178

Bbed> m/x 2c

File:/u01/app/oracle/oradata/orcl/system01.dbf (1)

block:60290 offsets:8178 to 8191 dba:0x0040eb82

------------------------------------------------------------------------

2c020106 4241444c 59390206 1e62

<32 bytes per line>

bbed> sum apply

Check value for File 1, Block 60290:

Current = 0xc7d4, required = 0xc7d4

Now, check out the library.

[Email protected]>alter system flush Buffer_cache;

System altered.

[Email Protected]>select * from Bbed_test;

X

--------------------

BADLY9

Jp

Be able to see that the deleted data has been restored back.

"Oracle" uses bbed to recover delete data