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

Vlado Barun

2005-01-15

Replies:
Thanks for the queries however they returned no rows, which I accutally
expected, since obj$ is not part of the c_obj# cluster, which is the cluster
that has the corrupted block (see my original post). So, I didn't even need
to use the alter session...

BTW, in the second and third query you need to adjust the index name...

So, what I did is to loop through each object in obj$ and try to access the
data. See code below. In this way I identified 3 tables, 2 views and a
synonym that are affected by the corrupted block. Fortunately, the three
tables are not needed anymore, and I should be able to rebuild the 2 views
and synonym.

So, my next question is what are my options in regards to resolving this
problem?

Currently, I see the following options:
1) As somebody mentioned before, if the row data and not the block header
data is corrupt, then by just dropping the objects, the corruption might go
away.
2) Create an empty database, export objects from corrupted database and
import all the objects into the new database.

I like option 1, but if it doesn't work is there any other less resource
intensive way to resolve this than option 2?


create or replace procedure access_all_data
as
l_sql_string varchar2(2000);
l_type  number;
l_object_name varchar2(30);
l_owner    varchar2(30);
l_cursor_name INTEGER;
l_ignore integer;
l_sqlerrm varchar2(4000);
l_row_count number;
cursor objs is
 select o.name object_name
     , o.type# type
     , u.name owner
 from sys.obj$ o
    , sys.user$ u
 where o.owner# = u.user#
 and u.name not in ('SYSTEM', 'SYS')
--  and rownum <11
 ORDER BY u.name, o.name;
begin
 for obj_rec in objs loop
   begin
     l_object_name:= obj_rec.object_name;
     l_owner:= obj_rec.owner;
     l_type:= obj_rec.type;
     
     l_sql_string:='select /*+ full(t) noparallel(t) */
count(*) from ' || l_owner || '.' || l_object_name || ' T';
      l_cursor_name := dbms_sql.open_cursor;
      dbms_sql.parse(l_cursor_name
             , l_sql_string
           , SYS.DBMS_SQL.native);
     DBMS_SQL.DEFINE_COLUMN(l_cursor_name, 1,
l_row_count);
      l_ignore := dbms_sql.execute(l_cursor_name);
     l_ignore := DBMS_SQL.FETCH_ROWS(l_cursor_name);
     DBMS_SQL.COLUMN_VALUE(l_cursor_name, 1,
l_row_count);
   
      dbms_sql.close_cursor(l_cursor_name);
     insert into object_avail(owner, object_name, type,
row_count)
     values (l_owner, l_object_name, l_type,
l_row_count);
   exception
      when others then
      l_sqlerrm := sqlerrm;
      insert into object_avail(owner, object_name, type,
error_msg)
      values (l_owner, l_object_name, l_type, l_sqlerrm);
      dbms_sql.close_cursor(l_cursor_name);
   end;
 end loop;
end;
/

Vlado Barun, M.Sc.
Mobile: 865 335 7652
AIM: vbarun2

-----Original Message-----
From: Parker, Matthew [mailto:matthewp@(protected)]
Sent: Friday, January 07, 2005 10:56 AM
To: vlado@(protected)
Subject: RE: Identifying the content of a corrupted block in system
tablespace

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=
paramter in bytes)
dd if=/u100/oradata/fstst/system01.dbf of=dd_df_1_bl_8002_curr.dd bs=8192
skip=8002 count=1 conv=notrunc

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


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

I have a corrupted block in the system tablespace.
I used the standard query to identify the object that the block but it
failed:

SQL>
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 = 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'

Then I did this:
ALTER SESSION SET EVENTS '10231 TRACE NAME CONTEXT FOREVER, LEVEL 10';

select owner
    , segment_name
    , segment_type
    , tablespace_name
    , block_id
    , blocks
from dba_extents
where file_id=1
and block_id in (
    select max(block_id)
    from dba_extents
    where file_id=1
    and block_id <= 8002
);

OWNER SEGMENT_NAME SEGMENT_TYPE TABLESPACE_NAME BLOCK_ID BLOCKS
----- ------------ ------------ ---------------- -------- ------
SYS  C_OBJ#     CLUSTER    SYSTEM       7978      25

So, the object that the corrupt block belongs to is c_obj#.

Is that correct?

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.
So, I'm trying to identify which object is lost.
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?

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...
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...


Vlado Barun, M.Sc.

Mobile: 865 335 7652

AIM: vbarun2





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