RE: Identifying the content of a corrupted block in system tablespace

  • From: "Parker, Matthew" <matthewp@xxxxxxxxxx>
  • To: <vlado@xxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Fri, 7 Jan 2005 08:55:46 -0800

Here are the three queries (Jeremiah was referring to, (nice to know =
your still having fun jeremiah although your company name is kind of =
funny)) in order to return the most data available, easily:

--So the the second part of the minus will bypass the bad block.
ALTER SESSION SET EVENTS '10231 TRACE NAME CONTEXT FOREVER, LEVEL 10';

select /*+ INDEX (o I_OBJ_1) */ obj# from obj$ o
minus
select /*+ FULL (o) */ obj# from obj$ o;

select /*+ INDEX (o I_OBJ_1) */ =
owner#,name,namespace,remoteowner,linkname,subname from obj$ o
minus
select /*+ FULL (o) */ =
owner#,name,namespace,remoteowner,linkname,subname from obj$ o;

select /*+ INDEX (o I_OBJ_1) */ oid$ from obj$ o
minus
select /*+ FULL (o) */ oid$ from obj$ o;


To fix this becomes more complex:
1. Does your friend have any backups of the database? How old are the =
backups? Is there a continuous redo chain for the backup?

2. Actual repair of the block would require at least a trace dump and a =
block dump.
alter system dump datafile '/u100/oradata/fstst/system01.dbf' block =
8002;
(You will need to fill in the appropriate database blocksize for the =
bs=3D paramter in bytes)
dd if=3D/u100/oradata/fstst/system01.dbf of=3Ddd_df_1_bl_8002_curr.dd =
bs=3D8192 skip=3D8002 count=3D1 conv=3Dnotrunc

Once this information is available then some choices can be made to fix =
the system.


-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx =
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Vlado Barun
Sent: Thursday, January 06, 2005 6:24 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Identifying the content of a corrupted block in system =
tablespace

I have a corrupted block in the system tablespace.=20
I used the standard query to identify the object that the block but it
failed:
=20
SQL>=20
  1  SELECT segment_name
  2      , segment_type
  3      , owner
  4      , tablespace_name
  5      , block_id
  6      , blocks
  7  FROM sys.dba_extents
  8  WHERE file_id =3D 1
  9* AND 8002 BETWEEN block_id and block_id + blocks -1 FROM =
sys.dba_extents
         *
ERROR at line 7:
ORA-01578: ORACLE data block corrupted (file # 1, block # 8002)
ORA-01110: data file 1: '/u100/oradata/fstst/system01.dbf'
=20
Then I did this:
ALTER SESSION SET EVENTS '10231 TRACE NAME CONTEXT FOREVER, LEVEL 10';
=20
select owner
       , segment_name
       , segment_type
       , tablespace_name
       , block_id
       , blocks
from dba_extents
where file_id=3D1
and block_id in (
        select max(block_id)
        from dba_extents
        where file_id=3D1
        and block_id <=3D 8002
);
=20
OWNER SEGMENT_NAME SEGMENT_TYPE TABLESPACE_NAME  BLOCK_ID BLOCKS
----- ------------ ------------ ---------------- -------- ------
SYS   C_OBJ#       CLUSTER      SYSTEM           7978         25
=20
So, the object that the corrupt block belongs to is c_obj#.=20
=20
Is that correct?
=20
If so, and since c_obj# stores data about objects (metadata), it =
basically means that I can not access the object whose metadata is in =
that block. =20
So, I'm trying to identify which object is lost.=20
For example, if it's just an index, I should be able to export all the =
objects from database into a new database and rebuild the index, and =
resolve the corruption in that way. Any idea how I can identify the =
object whose metadata is lost?=20
=20
I'm aware that Oracle support should be contacted, however a friend of =
mine asked me to look into  this before they contact Oracle Support =
since they don't have a support contract anymore...=20
BTW, this is 8.0.6, they identified this problem 3 months ago in their =
Peoplesoft application, and of course they don't have a good backup from =
which to recover...=20
=20

Vlado Barun, M.Sc.

Mobile: 865 335 7652

AIM: vbarun2

=20



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