Fix Corrupt Blocks: Block corruption

Oracle Tips by Lutz Hartmann

February 28, 2015

Question: I see an Oracle data block corruption in my alert log:

Hex dump of (file 6, block 88337) in trace file /d01/app/oracle/diag/rdbms/uat/trace/TESTUAT_dbw0_4469.trc
Corrupt block relative dba: 0x0181435911 (file 6, block 437)
Bad check value found during buffer corrupt after write
Data in bad block:

How do I fix a data file block corruption issue?

Answer: Oracle corruption is most frequently caused by a bad disk, although there are rare cases of "logical" corruption within the Oracle data blocks. You can use these steps to find the corrupt data blocks in Oracle. Oracle also provides a v$database_block_corruption view that you can check:

select * from v$database_block_corruption

If you know the file number and block number you can run the following query to see the exact data block that has corruption:

select
   relative_fno,
   owner,
   segment_name,
   segment_type
from
   dba_extents
where
   file_id = 6
and
   437 between block_id and block_id + blocks - 1;

Once you know the exact block ID you can view the corrupt block contents with the block editor BBED utility, working with Oracle technical support to repair the corruption.

If this is a production or test database, your first call should be to get the disk repaired and restored (if applicable) and to open a severity "one" service request on MOSC.

Oracle data corruption can occur in a table or index. Index corruption can be fixed by dropping and rebuilding the index (if possible) . You can also run some of the Oracle utilities for finding and fixing data corruption issues.

For additional information on handling corruption, see the BC expert notes on corruption and see MOSC Note 1088018.1 - Handling Oracle Database Corruption Issues.

There are three ways to repair corrupt blocks in Oracle:

   dbms_repair to repair corruption: dbms_repair to repair bad blocks

   BBED to repair corruption Using BBED to fix corrupt blocks

   RMAN repair corruption Repair corrupt Oracle block with RMAN

��