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Oracle® Database Recovery Manager Reference
10g Release 1 (10.1)

Part Number B10770-02
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BLOCKRECOVER

Syntax

blockrecover::=

Text description of blockrecover.gif follows


Text description of blockrecover

bmrBlockSpec::=

Text description of bmrBlockSpec.gif follows


Text description of bmrBlockSpec

bmrOption::=

Text description of bmrOption.gif follows


Text description of bmrOption

Purpose

Block media recovery recovers an individual data block or set of data blocks within a datafile. This type of recovery is useful if the data loss or corruption applies to a small number of blocks rather than to an entire datafile.

You can also use block media recovery to validate the integrity of redo generated after a backup. For example, you can do a trial-run block media recovery to detect problems in the archived redo stream.

Typically, block corruption is reported in error messages in trace files. Block-level data loss usually results from:

You need to specify the datafile number and block number or the tablespace and data block address (DBA) when executing the BLOCKRECOVER command, or use the CORRUPTION LIST keyword to recover all blocks reported in the V$DATABASE_BLOCK_CORRUPTION view.

Restrictions and Usage Notes

Keywords and Parameters

blockrecover
Syntax Element Description

DEVICE TYPE deviceSpecifier

Specifies the device type for the backup used in the block recovery.

See Also: "deviceSpecifier"

bmrBlockSpec
Syntax Element Description

bmrBlockSpec

Specifies the data blocks that require recovery.

CORRUPTION LIST

Recovers all blocks listed in the V$DATABASE_BLOCK_CORRUPTION view. This view displays blocks marked corrupt by the most recent BACKUP (with or without the VALIDATE option), VALIDATE, or CREATE CATALOG command. The following types of corruption result in rows added to this view:

  • Physical corruption (sometimes called media corruption). The database does not recognize the block at all: the checksum is invalid, the block contains all zeros, or the header and footer of the block do not match. Physical corruption checking is on by default, and can be turned off with the NOCHECKSUM option.
  • Logical corruption. The block has a valid checksum, the header and footer match, and so forth, but the contents are logically inconsistent. Logical corruption checking is off by default, and can be turned on with the CHECK LOGICAL option.

DATAFILE datafileSpec

Specifies a list of one or more datafiles that contain blocks requiring recovery.

See Also: "datafileSpec"

BLOCK integer

Specifies the block number of the block requiring media recovery. Typically, the block number is obtained from error message output.

TABLESPACE tablespace_name

Specifies the tablespace name or number containing the corrupt blocks.

DBA integer

Specifies the data block address (DBA) of the corrupt block.

bmrOption
Syntax Element Description

bmrOption

Specifies various restore options relating to the block recovery.

FROM BACKUPSET

Indicates that only backup sets should be restored.

FROM DATAFILECOPY

Indicates that only datafile image copies should be restored.

FROM TAG=
'tag_name'

Indicates that only the copy of the backup with the specified tag should be restored. Tag names are not case sensitive.

See Also: "BACKUP" to learn how a tag is applied to a copy of a backup.

RESTORE untilClause

Specifies that only backups and copies created before the specified time, SCN, or log sequence number should be restored.

See Also: "untilClause"

Examples

Recovering a Group of Corrupt Blocks: Example

This example recovers corrupt blocks in three datafiles:

BLOCKRECOVER DATAFILE 2 BLOCK 12, 13 DATAFILE 3 BLOCK 5, 98, 99 DATAFILE 4 BLOCK 19;
Limiting Block Media Recovery by Type of Restore: Example

The following example recovers a series of blocks and restores only from datafile copies:

RUN
{
  BLOCKRECOVER DATAFILE 3 BLOCK 2,3,4,5 TABLESPACE sales DBA 4194405, 4194409, 4194412
  FROM DATAFILECOPY;
}
Limiting Block Media Recovery by Backup Tag: Example

This example recovers blocks and restores only from the backup with the tag weekly_backup:

BLOCKRECOVER TABLESPACE SYSTEM DBA 4194404, 4194405 FROM TAG "weekly_backup";
Limiting Block Media Recovery by Time: Example

The following example recovers two blocks in the SYSTEM tablespace. It restores only from backups that could be used to recover the database to a point two days ago:

BLOCKRECOVER TABLESPACE SYSTEM DBA 4194404, 4194405 RESTORE UNTIL TIME 'SYSDATE-2';
Repairing All Block Corruption in the Database: Example

The following example runs a backup validation to populate V$DATABASE_BLOCK_CORRUPTION, then repairs any corrupt blocks recorded in the view:

BACKUP VALIDATE DATABASE;
BLOCKRECOVER CORRUPTION LIST;