This post discusses how to repair multiple or single block corruption of data files, including system data files, in an Oracle® database. Block corruption is a common source of database outages.
A database block is corrupted when its contents are different than what the Oracle database expects to find. If block corruption is not prevented or repaired, the corruption can bring down the database and possibly cause the loss of key business data.
This is one of the real time issues that you need to face and fix in production databases.
Find and fix block corruption
The following image shows a possible block corruption:
Image source: https://blog.toadworld.com/2017/12/01/block-corruption-in-an-oracle-database
Find the corruption
To find the corruption, execute the following commands:
SQL> select * from V$DATABASE_BLOCK_CORRUPTION;
FILE# BLOCK# BLOCKS CORRUPTION_CHANGE# CORRUPTION
----- ---------- ---------- ------------------ ----------
352 173191 9 0 ALL ZERO
SQL> SELECT FILE_ID,RELATIVE_FNO,FILE_NAME,TABLESPACE_NAME FROM DBA_DATA_FILES WHERE FILE_ID=352;
FILE_ID RELATIVE_FNO FILE_NAME TABLESPACE_NAME
---------- ------------ -------------------------------------------------- ------------------
352 352 /u01/apps_st/samusxxxxxxxx_data2/system09.dbf SYSTEM
SQL> SELECT owner, segment_name, segment_type FROM dba_extents WHERE RELATIVE_FNO = 352 AND Block_id BETWEEN 173191 AND 173191 + blocks - 1;
OWNER SEGMENT_NAME SEGMENT_TYPE
-------- --------------- ------------------
SYS I_COL3 INDEX
SYS C_OBJ# CLUSTER
Note: In this case, SYS object segment I_COL3 has a block corruption. The
corrupted block, as reported by the dbv command, is shown as free in the
dba_free_space view.
Free the blocks
To free the blocks for file 352, execute the following commands:
SQL> select * from V$DATABASE_BLOCK_CORRUPTION;
FILE# BLOCK# BLOCKS CORRUPTION_CHANGE# CORRUPTION
----- ---------- ---------- ------------------ ----------
352 173191 9 0 ALL ZERO
SQL> Select * from dba_free_space where file_id =352 and 173191 between block_id and block_id + blocks -1;
TABLESPACE_NAME FILE_ID BLOCK_ID BYTES BLOCKS RELATIVE_FNO
--------------- ------- -------- ----- ---------- ------------
SYSTEM 352 173191 73728 9 352
Force clear blocks
After the blocks are free, you can use the following commands to force clear those corrupted blocks. This is also known as formatting corrupted blocks that are not part of any segment.
1. Create a user and grant the user access to the database.
create user Scott identified by password default tablespace SYSTEM;
grant resource, connect, create table, create trigger to Scott;
2. Identify the corrupt block against the data file
[Thu Nov 17 11:59:19 orbdev@samusxxxxxxxx:~ ] $ dbv file='/mnt/apps_st/samusxxxxxxxx_data2/system09.dbf' userid=sys/xxxxx
DBVERIFY: Release 11.2.0.4.0 - Production on Thu Nov 17 11:59:21 2016
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
DBVERIFY - Verification starting: FILE = /mnt/apps_st/samusxxxxxxxx_data2/system09.dbf
Page 173191 is marked corrupt
Corrupt block relative dba: 0x5802a487 (file 352, block 173191)
Completely zero block found during dbv:
Page 173192 is marked corrupt
Corrupt block relative dba: 0x5802a488 (file 352, block 173192)
Completely zero block found during dbv:
Page 173193 is marked corrupt
Corrupt block relative dba: 0x5802a489 (file 352, block 173193)
Completely zero block found during dbv:
Page 173194 is marked corrupt
Corrupt block relative dba: 0x5802a48a (file 352, block 173194)
Completely zero block found during dbv:
Page 173195 is marked corrupt
Corrupt block relative dba: 0x5802a48b (file 352, block 173195)
Completely zero block found during dbv:
Page 173196 is marked corrupt
Corrupt block relative dba: 0x5802a48c (file 352, block 173196)
Completely zero block found during dbv:
Page 173197 is marked corrupt
Corrupt block relative dba: 0x5802a48d (file 352, block 173197)
Completely zero block found during dbv:
Page 173198 is marked corrupt
Corrupt block relative dba: 0x5802a48e (file 352, block 173198)
Completely zero block found during dbv:
Page 173199 is marked corrupt
Corrupt block relative dba: 0x5802a48f (file 352, block 173199)
Completely zero block found during dbv:
DBVERIFY - Verification complete
Total Pages Examined : 917504
Total Pages Processed (Data): 253735
Total Pages Failing (Data) : 0
Total Pages Processed (Index): 335744
Total Pages Failing (Index): 0
Total Pages Processed (Other): 375
Total Pages Processed (Seg) : 17
Total Pages Failing (Seg) : 0
Total Pages Empty : 327624
Total Pages Marked Corrupt : 9
Total Pages Influx : 0
Total Pages Encrypted : 0
Highest block SCN : 3412538527 (1421.3412538527)
[Thu Nov 17 12:00:13 orbdev@samusxxxxxxxx:~ ] $
3. Find the free space
Select * from dba_free_space where file_id= <Absolute file number> and <corrupted block number> between block_id and block_id + blocks -1;
SQL> Select * from dba_free_space where file_id=352 and 173191 between block_id and block_id + blocks -1;
TABLESPACE_NAME FILE_ID BLOCK_ID BYTES BLOCKS RELATIVE_FNO
--------------- ---------- ---------- ---------- --------- ------------
SYSTEM 352 173196 73728 9 352
4. Reformat first corrupted block
Repeat step 4 until all corrupted blocks are reformatted.
create table scott.s (n number,c varchar2(4000)) nologging tablespace SYSTEM;
select owner,table_name,tablespace_name from dba_tables where table_name='S';
SQL> CREATE OR REPLACE TRIGGER corrupt_trigger
AFTER INSERT ON scott.s
REFERENCING OLD AS p_old NEW AS new_p
FOR EACH ROW
DECLARE
corrupt EXCEPTION;
BEGIN
IF (dbms_rowid.rowid_block_number(:new_p.rowid)=&blocknumber)
and (dbms_rowid.rowid_relative_fno(:new_p.rowid)=&filenumber) THEN
RAISE corrupt;
END IF;
EXCEPTION
WHEN corrupt THEN
RAISE_APPLICATION_ERROR(-20000, 'Corrupt block has been formatted');
END;
/
Enter value for blocknumber: 173191
old 8: IF (dbms_rowid.rowid_block_number(:new_p.rowid)=&blocknumber)
new 8: IF (dbms_rowid.rowid_block_number(:new_p.rowid)=173191)
Enter value for filenumber: 352
old 9: and (dbms_rowid.rowid_relative_fno(:new_p.rowid)=&filenumber) THEN
new 9: and (dbms_rowid.rowid_relative_fno(:new_p.rowid)=352) THEN
Trigger created.
Select BYTES/1024/1024 from dba_free_space where file_id=352 and 173191 between block_id and block_id + blocks -1;
72K
SQL> BEGIN
FOR i IN 1..100000 LOOP
EXECUTE IMMEDIATE 'alter table scott.s allocate extent (DATAFILE '||'''/mnt/apps_st/samusxxxxxxxx_data2/system09.dbf''' ||'SIZE 72K)';
END LOOP;
END;
/
SQL> BEGIN
FOR i IN 1..1000000 LOOP
INSERT /*+ APPEND */ INTO scott.s select i, lpad('REFORMAT',3092, 'R') from dual;
commit ;
END LOOP;
END;
/
SQL> Select * from v$database_block_corruption;
no rows selected
DROP TABLE scott.s;
Alter system switch logfile;
Alter system checkpoint;
DROP trigger corrupt_trigger;
5. Verify that the corrupted blocks are fixed
SQL> select * from V$DATABASE_BLOCK_CORRUPTION;
no rows selected
[Wed Nov 16 08:12:37 orbdev@samusxxxxxx:~ ] $ dbv file='/mnt/apps_st/samusxxxxxx_data2/system09.dbf' userid=sys/****
DBVERIFY: Release 11.2.0.4.0 - Production on Wed Nov 16 08:12:41 2016
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
DBVERIFY - Verification starting : FILE = /mnt/apps_st/samusxxxxxx_data2/system09.dbf
DBVERIFY - Verification complete
Total Pages Examined : 655359
Total Pages Processed (Data) : 260868
Total Pages Failing (Data) : 0
Total Pages Processed (Index): 340482
Total Pages Failing (Index): 0
Total Pages Processed (Other): 278
Total Pages Processed (Seg): 15
Total Pages Failing (Seg): 0
Total Pages Empty : 53716
Total Pages Marked Corrupt : 0
Total Pages Influx : 0
Total Pages Encrypted : 0
Highest block SCN : 136830000 (1422.136830000)
[Wed Nov 16 08:14:50 orbldev2@samusxxxxxx:~ ] $
Conclusion
To detect and prevent data corruption, perform the following Maximum Availability Architecture (MAA) best practices:
- Use Oracle Data Guard.
- Set the Oracle Database block corruption detection parameters.
- Implement a backup and recovery strategy with Recovery Manager (RMAN).
These high availability solutions are integrated with Oracle Database and take advantage of the underlying data structures. Thus, the tools offer a new class of intelligent data protection and disaster recovery.
Use the Feedback tab to make any comments or ask questions.
Learn more about our database services and Rackspace Application services.