I want to corrupt a datablock(!)

Hi there,
ok, I want to do a demo of how to recover if you get a block corruption, and need to use dbms_repair & rowid scans to retrieve as much data as poss etc.

To do that I need to corrupt a single block in a datafile on unix, and this is where im stuck....

Anyone out there have any ideas how to do this. I have an idea I can use dd to copy the file out and then edit in Vi, and the use dd to put it back... or something - dunno. Any advice would be usefull...

ta lots, Bob

Ask a developer.

Where is gandolf when you need him?

Hmm....
.... I posted a Tar as well - I would be amazed if Oracle Support comes back with anything usefull though...

need to find a block editor

maybe od could do it

Got a magnet?

http://www.freedownloadscenter.com/B...ditor-hex.html

I've seen it done, but it was long ago. How you know which bytes to change is a mystery to me. Guess you could just change away till analyze table validate structure turns up a corrupt block.

Maybe gandolf is off getting his hair bleached.
"Gandalf the Grey" becomes "Gandalf the White"

-Ken

Hi

Just open a small datafile in notepad and save it.The block should be corrupted

regards
Hrishy

Quote:

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Originally posted by Mr.Hanky
Ask a developer.

Where is gandolf when you need him?

---

Somehow when you think corrupt, my name comes up? :rolleyes: I would have thought that you would have been smart enough to know that any editor can corrupt a datafile. In fact I would have assumed that you had already practiced that! :D

Oracle itself provides a tool called bbed.
Normally Oracle support use it for repairing blocks. Of course, you can use to corrupt blocks.

You need to compile bbed urself.
$ cd $ORACLE_HOME/rdbms/lib
$ make -f ins_rdbms.mk $ORACLE_HOME/rdbms/lib/bbed

Thanks

thats cool hun:)
But i still dont know how to use it (after compiling):D

Cheers guys - lots to look at there. Corruptnig a datafile is easy, its the screwing of a single block that im after - theres a few things thre I shal try. If I get a decent result I will update!

ta lots,
Bob

I suggest you dont use that, asking for a world of trouble with it

Quote:

---

Originally posted by bmycroft
Cheers guys - lots to look at there. Corruptnig a datafile is easy, its the screwing of a single block that im after - theres a few things thre I shal try. If I get a decent result I will update!

ta lots,
Bob

---

here is a way which will work on unix (nicked from the oracle-l list)

Code:

---

create tablespace corrupt datafile '/u01/oradata/dv03/corrupt.dbf' size 5m
reuse
extent management local uniform size 8k
/

-- create a table with 2 blocks
create table corrupt_objects
tablespace corrupt
as
select *
from all_objects
where rownum < 70
/

-- get the block id
select segment_type, relative_fno, file_id, extent_id, block_id, blocks
from dba_extents
where segment_name = 'CORRUPT_OBJECTS'
/

SEGMENT_TYPE RELATIVE_FNO FILE_ID EXTENT_ID BLOCK_ID BLOCKS
------------------ ------------ ---------- ---------- ---------- -----------
TABLE 10 10 0 9 2

1 row selected.

#corrupt one block
dd conv=notrunc if=/dev/zero of=/u01/oradata/dv03/corrupt.dbf bs=8192
seek=10 count=1

-- check for corrupt block
declare
v_corrupt_count integer;
begin
sys.dbms_repair.check_object (
schema_name => 'JS001292',
object_name => 'CORRUPT_OBJECTS',
repair_table_name => 'REPAIR_TABLE',
object_type => sys.dbms_repair.table_object,
corrupt_count => v_corrupt_count
);

dbms_output.put_line('Corrupt Count: ' || v_corrupt_count);
end;
/

Corrupt Count: 1

PL/SQL procedure successfully completed.

-- examine corruptions

SQL> select schema_name,object_name, corrupt_type
from sys.repair_table


SCHEMA_NAME OBJECT NAME CORRUPT_TYPE
------------------------------ ------------------------------ ------------
JS001292 CORRUPT_OBJECTS 6148
JS001292 CORRUPT_OBJECTS 6148

2 rows selected.

---

Cool. That looks a lot more user-friendly than using bbed. I guessed the password for bbed by the way, I may have to have a play with it later on. Just for those of yuo who are worried - I would NEVER EVER use it on a live system, trust me.... Oh ye Gods no. Just gives me the shivers thinking about it :-)

I shall try the method using dd I think and then go back and look at the bed stuff later somewhere safe...

Cheers lots or the help guys, I do appreciate it

-B

Excellent :-) using dd to overright specific blocks works a treat.

Using bbed ; I get close but wen I try the corrupt command, I get a core dump. Bit of a shame but no great problem as i can use dd.

ta lots,
Bob