DBVERIFY

It is an external command-line utility that performs a physical data structure integrity check. It can be used on offline or online databases, as well on backup files.
You use DBVERIFY primarily when you need to ensure that a backup database (or datafile) is valid before it is restored, or as a diagnostic aid when you have encountered data corruption problems.

Overview:

• Verifying the table and tablespaces
• Checking the header block for the table
• Stimulating a corruption
• Recovering the block using RMAN
• Verifying using DATABASE BLOCK CORRUPTION

Step 1:

Verifying the TABLESPACE_NAME and its associated SEGMENT_NAME.

SQL> select SEGMENT_NAME,TABLESPACE_NAME from dba_segments where OWNER=’SCOTT’;

SEGMENT_NAME TABLESPACE_NAME
————— ——————————
SALGRADE USERS
DEPT USERS
EMP USERS
PK_DEPT USERS
PK_EMP USERS

Step 2:

By issuing the below command we can check the header block for the table ‘DEPT’

SELECT header_block FROM dba_segments WHERE segment_name=’DEPT’;

SQL> select file_name from dba_data_files;

FILE_NAME

/u01/app/oracle/oradata/ORACLE19C/datafile/o1_mf_users_j21snyfk_.dbf
/u01/app/oracle/oradata/ORACLE19C/datafile/o1_mf_undotbs1_j21snxbn_.dbf
/u01/app/oracle/oradata/ORACLE19C/datafile/o1_mf_system_j21skfkg_.dbf
/u01/app/oracle/oradata/ORACLE19C/datafile/o1_mf_sysaux_j21sn40n_.dbf

Step 3:

Command to corrupt the block ,

[oracle@oracle19c ~]$ dd of=/u01/app/oracle/oradata/ORACLE19C/datafile/o1_mf_users_j21snyfk_.dbf bs=8192 conv=notrunc seek=347 << EOF

corruption test
EOF
0+1 records in
0+1 records out
16 bytes (16 B) copied, 4.9494e-05 s, 323 kB/s

Step 4:

To flush the buffer cache we need to provide the below command

SQL> ALTER SYSTEM FLUSH BUFFER_CACHE;

System altered.

Step 5:

Selecting the corrupted table , but it shows error

Step 6:

Viewing the corrected block in the database

select * from V$DATABASE_BLOCK_CORRUPTION;

Step 7:

Command to verify the corrupted block across the datafile using the below command

dbv file=/u01/app/oracle/oradata/ORACLE19C/datafile/o1_mf_users_j21snyfk_.dbf blocksize=8192

Step 8:

Command to recover the block and datafile using RMAN,
The datafile and corrupted block we can check it in the previous step ‘DBVERIFY-DBV’ command

recover datafile 7 block 347;

Verification’s:

After recovering there are no rows found in database block corruption ,
And after issuing dbverify command ,there we can see the marked corruption is ‘0’

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