Oracle Repair Table Block Detecting Corruption

Examples: Building a Repair Table or Orphan Key Table

The ADMIN_TABLE procedure is used to create, purge, or drop a repair table or an orphan key table.

A repair table provides information about the corruptions that were found by the CHECK_OBJECT procedure and how these will be addressed if the FIX_CORRUPT_BLOCKS procedure is run. Further, it is used to drive the execution of the FIX_CORRUPT_BLOCKS procedure.

An orphan key table is used when the DUMP_ORPHAN_KEYS procedure is executed and it discovers index entries that point to corrupt rows. The DUMP_ORPHAN_KEYS procedure populates the orphan key table by logging its activity and providing the index information in a usable manner.

Example: Creating a Repair Table
The following example creates a repair table for the users tablespace.

BEGIN
DBMS_REPAIR.ADMIN_TABLES (
TABLE_NAME => 'REPAIR_TABLE',
TABLE_TYPE => dbms_repair.repair_table,
ACTION => dbms_repair.create_action,
TABLESPACE => 'USERS');
END;
/
For each repair or orphan key table, a view is also created that eliminates any rows that pertain to objects that no longer exist. The name of the view corresponds to the name of the repair or orphan key table and is prefixed by DBA_ (for example, DBA_REPAIR_TABLE or DBA_ORPHAN_KEY_TABLE).

The following query describes the repair table that was created for the users tablespace.

DESC REPAIR_TABLE

Name Null? Type
---------------------------- -------- --------------
OBJECT_ID NOT NULL NUMBER
TABLESPACE_ID NOT NULL NUMBER
RELATIVE_FILE_ID NOT NULL NUMBER
BLOCK_ID NOT NULL NUMBER
CORRUPT_TYPE NOT NULL NUMBER
SCHEMA_NAME NOT NULL VARCHAR2(30)
OBJECT_NAME NOT NULL VARCHAR2(30)
BASEOBJECT_NAME VARCHAR2(30)
PARTITION_NAME VARCHAR2(30)
CORRUPT_DESCRIPTION VARCHAR2(2000)
REPAIR_DESCRIPTION VARCHAR2(200)
MARKED_CORRUPT NOT NULL VARCHAR2(10)
CHECK_TIMESTAMP NOT NULL DATE
FIX_TIMESTAMP DATE
REFORMAT_TIMESTAMP DATE
Example: Creating an Orphan Key Table
This example illustrates the creation of an orphan key table for the users tablespace.

BEGIN
DBMS_REPAIR.ADMIN_TABLES (
TABLE_NAME => 'ORPHAN_KEY_TABLE',
TABLE_TYPE => dbms_repair.orphan_table,
ACTION => dbms_repair.create_action,
TABLESPACE => 'USERS');
END;
/
The orphan key table is described in the following query:

DESC ORPHAN_KEY_TABLE

Name Null? Type
---------------------------- -------- -----------------
SCHEMA_NAME NOT NULL VARCHAR2(30)
INDEX_NAME NOT NULL VARCHAR2(30)
IPART_NAME VARCHAR2(30)
INDEX_ID NOT NULL NUMBER
TABLE_NAME NOT NULL VARCHAR2(30)
PART_NAME VARCHAR2(30)
TABLE_ID NOT NULL NUMBER
KEYROWID NOT NULL ROWID
KEY NOT NULL ROWID
DUMP_TIMESTAMP NOT NULL DATE

Example: Detecting Corruption
The CHECK_OBJECT procedure checks the specified object, and populates the repair table with information about corruptions and repair directives. You can optionally specify a range, partition name, or subpartition name when you want to check a portion of an object.

Validation consists of checking all blocks in the object that have not previously been marked corrupt. For each block, the transaction and data layer portions are checked for self consistency. During CHECK_OBJECT, if a block is encountered that has a corrupt buffer cache header, then that block is skipped.

The following is an example of executing the CHECK_OBJECT procedure for the scott.dept table.

SET SERVEROUTPUT ON
DECLARE num_corrupt INT;
BEGIN
num_corrupt := 0;
DBMS_REPAIR.CHECK_OBJECT (
SCHEMA_NAME => 'SCOTT',
OBJECT_NAME => 'DEPT',
REPAIR_TABLE_NAME => 'REPAIR_TABLE',
CORRUPT_COUNT => num_corrupt);
DBMS_OUTPUT.PUT_LINE('number corrupt: ' || TO_CHAR (num_corrupt));
END;
/
SQL*Plus outputs the following line, indicating one corruption:

number corrupt: 1
Querying the repair table produces information describing the corruption and suggesting a repair action.

SELECT OBJECT_NAME, BLOCK_ID, CORRUPT_TYPE, MARKED_CORRUPT,
CORRUPT_DESCRIPTION, REPAIR_DESCRIPTION
FROM REPAIR_TABLE;

OBJECT_NAME BLOCK_ID CORRUPT_TYPE MARKED_COR
------------------------------ ---------- ------------ ----------
CORRUPT_DESCRIPTION
------------------------------------------------------------------------------
REPAIR_DESCRIPTION
------------------------------------------------------------------------------
DEPT 3 1 FALSE
kdbchk: row locked by non-existent transaction
table=0 slot=0
lockid=32 ktbbhitc=1
mark block software corrupt
The corrupted block has not yet been marked corrupt, so this is the time to extract any meaningful data. After the block is marked corrupt, the entire block must be skipped.

Example: Fixing Corrupt Blocks
Use the FIX_CORRUPT_BLOCKS procedure to fix the corrupt blocks in specified objects based on information in the repair table that was generated by the CHECK_OBJECT procedure. Before changing a block, the block is checked to ensure that the block is still corrupt. Corrupt blocks are repaired by marking the block software corrupt. When a repair is performed, the associated row in the repair table is updated with a timestamp.

This example fixes the corrupt block in table scott.dept that was reported by the CHECK_OBJECT procedure.

SET SERVEROUTPUT ON
DECLARE num_fix INT;
BEGIN
num_fix := 0;
DBMS_REPAIR.FIX_CORRUPT_BLOCKS (
SCHEMA_NAME => 'SCOTT',
OBJECT_NAME=> 'DEPT',
OBJECT_TYPE => dbms_repair.table_object,
REPAIR_TABLE_NAME => 'REPAIR_TABLE',
FIX_COUNT=> num_fix);
DBMS_OUTPUT.PUT_LINE('num fix: ' || TO_CHAR(num_fix));
END;
/
SQL*Plus outputs the following line:

num fix: 1
The following query confirms that the repair was done.

SELECT OBJECT_NAME, BLOCK_ID, MARKED_CORRUPT
FROM REPAIR_TABLE;

OBJECT_NAME BLOCK_ID MARKED_COR
------------------------------ ---------- ----------
DEPT 3 TRUE
Example: Finding Index Entries Pointing to Corrupt Data Blocks
The DUMP_ORPHAN_KEYS procedure reports on index entries that point to rows in corrupt data blocks. For each index entry, a row is inserted into the specified orphan key table. The orphan key table must have been previously created.

This information can be useful for rebuilding lost rows in the table and for diagnostic purposes.

Note:

This should be run for every index associated with a table identified in the repair table.
In this example, pk_dept is an index on the scott.dept table. It is scanned to determine if there are any index entries pointing to rows in the corrupt data block.

SET SERVEROUTPUT ON
DECLARE num_orphans INT;
BEGIN
num_orphans := 0;
DBMS_REPAIR.DUMP_ORPHAN_KEYS (
SCHEMA_NAME => 'SCOTT',
OBJECT_NAME => 'PK_DEPT',
OBJECT_TYPE => dbms_repair.index_object,
REPAIR_TABLE_NAME => 'REPAIR_TABLE',
ORPHAN_TABLE_NAME=> 'ORPHAN_KEY_TABLE',
KEY_COUNT => num_orphans);
DBMS_OUTPUT.PUT_LINE('orphan key count: ' || TO_CHAR(num_orphans));
END;
/
The following output indicates that there are three orphan keys:

orphan key count: 3
Index entries in the orphan key table implies that the index should be rebuilt. This guarantees that a table probe and an index probe return the same result set.

Example: Skipping Corrupt Blocks
The SKIP_CORRUPT_BLOCKS procedure enables or disables the skipping of corrupt blocks during index and table scans of the specified object. When the object is a table, skipping applies to the table and its indexes. When the object is a cluster, it applies to all of the tables in the cluster, and their respective indexes.

The following example enables the skipping of software corrupt blocks for the scott.dept table:

BEGIN
DBMS_REPAIR.SKIP_CORRUPT_BLOCKS (
SCHEMA_NAME => 'SCOTT',
OBJECT_NAME => 'DEPT',
OBJECT_TYPE => dbms_repair.table_object,
FLAGS => dbms_repair.skip_flag);
END;
/
Querying scott's tables using the DBA_TABLES view shows that SKIP_CORRUPT is enabled for table scott.dept.

SELECT OWNER, TABLE_NAME, SKIP_CORRUPT FROM DBA_TABLES
WHERE OWNER = 'SCOTT';

OWNER TABLE_NAME SKIP_COR
------------------------------ ------------------------------ --------
SCOTT ACCOUNT DISABLED
SCOTT BONUS DISABLED
SCOTT DEPT ENABLED
SCOTT DOCINDEX DISABLED
SCOTT EMP DISABLED
SCOTT RECEIPT DISABLED
SCOTT SALGRADE DISABLED
SCOTT SCOTT_EMP DISABLED
SCOTT SYS_IOT_OVER_12255 DISABLED
SCOTT WORK_AREA DISABLED

10 rows selected.