Block Browser and Editor on Linux with Oracle 10g R2 database

Article [1] has been written in French, contains two interesting examples .
The posting bellow is supposed to be a translation final part from [1] to English,
dealing with other tables from sample schemas loaded during standard installation.
However , the way to obtain oracle's file number and block number for particular
record from selected table is different from [1].
We also focus attention at index corruption after changing field's value or record
recovery by BBED.


1.Modifying field's value for particular record in hr.departments table.


Get file number and header block for table hr.departments:-

 select owner,segment_name,header_file,header_block,blocks
 from dba_segments
 where owner='HR' and segment_name='DEPARTMENTS';
 

OWNER    SEGMENT_NAME    HEADER_FILE    HEADER_BLOCK     BLOCKS
-------          -------------------          --------------------      ----------------------        -------------
SCOTT          EMP                              5                   55                              8
  

Getting block number of record, supposed to be changed, with dbms_rowid package:-

Searching for offset of the pattern:-

Run "modify /c Abcdefg" to replace "Support" :-

Update block's checksum:-

Verify data with select statement:-

SQL> alter system flush buffer_cache;
  

To force Oracle perform reading block from disk device,not from buffer cache.

2.Recovering deleted record from scott.emp.


Get file number and header block for table scott.emp:-

 select owner,segment_name,header_file,header_block,blocks
 from dba_segments
 where owner='SCOTT' and segment_name='EMP';
 

OWNER   SEGMENT_NAME   HEADER_FILE      HEADER_BLOCK      BLOCKS
------          -----------                   -------------               --------------                   ------
SCOTT        EMP                         4                           27                            8
  

Get the block number contains record with ename='JAMES' like in previous example.
Then search for word 'JAMES' to get it's offset.



Make dump with offset=offset-16 and look for first byte of the record (0x2c)
Watch the value of first byte of record when it got deleted.




First byte of deleted record appears to be changed to hexadecimal 0x3c.
The intend is to put 0x2c back on it's place as the first byte of deleted record.

SQL> delete from emp where ename='JAMES';

1 row deleted.

SQL> commit;

Commit complete.
  

Run "modify /x 2c" in bbed:-

Update block's checksum:-

Restart Oracle instance:-

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup;
ORACLE instance started.

Total System Global Area  285212672 bytes
Fixed Size                  1218968 bytes
Variable Size              83887720 bytes
Database Buffers          192937984 bytes
Redo Buffers                7168000 bytes
Database mounted.
Database opened.
  

Or just:-

SQL> alter system flush buffer_cache;
 

To force Oracle perform reading block from disk device,not from buffer cache.


Check for undeleted record:-

SQL> conn scott/tiger@orcl;
Connected.

SQL> select * from emp where ename='JAMES';

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM
---------- ---------- --------- ---------- --------- ---------- ----------
    DEPTNO
----------
      7900 JAMES      CLERK           7698 03-DEC-81        950
        30

SQL> select * from emp where empno=7900;
no rows selected
  

At this point it became quite clear , that we have to recreate any indexes on table,
which records have been recovered by BBED.They are no longer valid.
Same issue will be in place regarding indexes based on columns have been modified by BBED.
Recreate index on empno field of emp table:-

SQL> alter table emp drop constraint PK_EMP;

Table altered.

SQL> alter table emp add  constraint PK_EMP primary key(empno);

Table altered.

SQL> select * from emp where empno=7900;

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM
---------- ---------- --------- ---------- --------- ---------- ----------
    DEPTNO
----------
      7900 JAMES      CLERK           7698 03-DEC-81        950
        30
  

References.


1.http://mbouayoun.developpez.com/bbed/
2.http://orafaq.com/papers/dissassembling_the_data_block.pdf

Block browse and edit utility (BBED) in Oracle 10g R2 on Linux

First login as oracle to compile bbed:

$ cd  $ORACLE_HOME/rdbms/lib
$ make -f ins_rdbms.mk $ORACLE_HOME/rdbms/lib/bbed
$ls -la bbed
$ cp $ORACLE_HOME/rdbms/lib/bbed $ORACLE_HOME/bin
   

Use any hexadecimal editor on Linux to discover password
needed to start bbed:-

[oracle@ServerORCL orcl]$ bbed
Password:
BBED: Release 2.0.0.0.0 - Limited Production on Sun Jul 15 14:17:39 2007

Copyright (c) 1982, 2005, Oracle.  All rights reserved.

************* !!! For Oracle Internal Use only !!! ***************

BBED> show
        FILE#           0
        BLOCK#          1
        OFFSET          0
        DBA             0x00000000 (0 0,1)
        FILENAME
        BIFILE          bifile.bbd
        LISTFILE
        BLOCKSIZE       8192
        MODE            Browse
        EDIT            Unrecoverable
        IBASE           Dec
        OBASE           Dec
        WIDTH           80
        COUNT           512
        LOGFILE         log.bbd
        SPOOL           No
  

Next run as sysdba:-

SQL> select owner,segment_name,header_file,header_block,blocks
  2  from dba_segments
  3  where owner='HR' and segment_name='DEPARTMENTS';

OWNER
------------------------------
SEGMENT_NAME
-----------------------------------
HEADER_FILE HEADER_BLOCK     BLOCKS
----------- ------------ ----------
HR
DEPARTMENTS
          5           51          8
   

Tune BBED properly to perform block corruption for hr.departments table.

BBED> set listfile '/home/oracle/bbed.log'
        LISTFILE        /home/oracle/bbed.log
BBED> set blocksize 8192
        BLOCKSIZE       8192
BBED> set filename '/u02/oradata/orcl/example01.dbf'
BBED> set dba 5,52
BBED> set mode edit
BBED> show
        FILE#           5
        BLOCK#          52
        OFFSET          0
        DBA             0x01400034 (20971572 5,52)
        FILENAME        /u02/oradata/orcl/example01.dbf
        BIFILE          bifile.bbd
        LISTFILE        /home/oracle/bbed.log
        BLOCKSIZE       8192
        MODE            Edit
        EDIT            Unrecoverable
        IBASE           Dec
        OBASE           Dec
        WIDTH           80
        COUNT           64
        LOGFILE         log.bbd
        SPOOL           No
   

[oracle@ServerORCL ~]$ cat bbed.log
1 /u02/oradata/orcl/system01.dbf   503316480
2 /u02/oradata/orcl/undotbs01.dbf  41943040
3 /u02/oradata/orcl/sysaux01.dbf   262144000
4 /u02/oradata/orcl/users01.dbf    5242880
5 /u02/oradata/orcl/example01.dbf  104857600
  

Replace second block of table

BBED> set offset 0
        OFFSET          0

BBED> copy dba 5,10 to dba 5,52
 File: /u02/oradata/orcl/example01.dbf (5)
 Block: 52               Offsets:    0 to   63           Dba:0x01400034
------------------------------------------------------------------------
 21a20000 0a004001 0ed00600 00000104 414e0000 00000000 00000000 00000000
 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
  

Restart Oracle instance.

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup;
ORACLE instance started.

Total System Global Area  285212672 bytes
Fixed Size                  1218968 bytes
Variable Size              75499112 bytes
Database Buffers          201326592 bytes
Redo Buffers                7168000 bytes
Database mounted.
Database opened.
    

Connect as HR to get block corruption error
when SELECT * FROM DEPARTMENTS.
Then start rman:-

RMAN> connect target /
RMAN> run {BACKUP VALIDATE DATABASE;}
Starting backup at 15-JUL-07
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=141 devtype=DISK
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
input datafile fno=00001 name=/u02/oradata/orcl/system01.dbf
input datafile fno=00003 name=/u02/oradata/orcl/sysaux01.dbf
input datafile fno=00005 name=/u02/oradata/orcl/example01.dbf
input datafile fno=00002 name=/u02/oradata/orcl/undotbs01.dbf
input datafile fno=00004 name=/u02/oradata/orcl/users01.dbf
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:35
channel ORA_DISK_1: starting full datafile backupset
channel ORA_DISK_1: specifying datafile(s) in backupset
including current control file in backupset
including current SPFILE in backupset
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:02
Finished backup at 15-JUL-07
    

Run query as SYSDBA

select * from V$backup_corruption;


     RECID      STAMP  SET_STAMP  SET_COUNT     PIECE#      FILE#     BLOCK#
---------- ---------- ---------- ---------- ---------- ---------- ----------
    BLOCKS CORRUPTION_CHANGE# MAR CORRUPTIO
---------- ------------------ --- ---------
         7  628005346  628005315          9          1          5         52
         1                  0 YES CORRUPT
  

Proceed with RMAN block recovery

RMAN> run {blockrecover datafile 5  block 52;}

Starting blockrecover at 15-JUL-07
using channel ORA_DISK_1

channel ORA_DISK_1: restoring block(s)
channel ORA_DISK_1: specifying block(s) to restore from backup set
restoring blocks of datafile 00005
channel ORA_DISK_1: reading from backup piece
/u01/app/oracle/flash_recovery_area/ORCL/backupset/2007_07_15/
o1_mf_nnndf_TAG20070715T105801_39mkctc7_.bkp
channel ORA_DISK_1: restored block(s) from backup piece 1 piece
handle=/u01/app/oracle/flash_recovery_area/ORCL/backupset/2007_07_15/
o1_mf_nnndf_TAG20070715T105801_39mkctc7_.bkp
tag=TAG20070715T105801
channel ORA_DISK_1: block restore complete, elapsed time: 00:00:07
starting media recovery
media recovery complete, elapsed time: 00:00:03
Finished blockrecover at 15-JUL-07
   

Connect as HR to perform SELECT * FROM DEPARTMENTS without errors.