BLOCKRECOVER

Syntax

Text description of the illustration blockrec.gif

bmrBlockSpec::=

Text description of the illustration bmrblock.gif

bmrOption::=

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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 Oracle error messages in trace files. Block-level data loss usually results from:

• I/O errors causing minor data loss

• Memory corruptions that get flushed to disk

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$BACKUP_CORRUPTION and V$COPY_CORRUPTION views.

See Also: Oracle9i Recovery Manager User's Guide for concepts and Oracle9i Recovery Manager User's Guide for procedures

Restrictions and Usage Notes

• This command is available only in the Enterprise Edition of Oracle9i.

• The target database must be mounted or open. Note that you do not have to take a datafile offline if you are performing block recovery on it.

• You can only perform complete recovery of individual blocks. Point-in-time recovery of individual data blocks is not supported.

• You can only perform block media recovery on corrupt blocks.

• Blocks marked media corrupt are not accessible until recovery completes.

• You cannot perform block media recovery by using a backup control file.

• You must have a full backup of the file containing the corrupt blocks: block media recovery cannot use incremental backups.

• Block media recovery cannot survive a missing or inaccessible archived log, although it can sometimes survive missing or inaccessible records (see Oracle9i Recovery Manager User's Guide).

• The datafile header block (block 1) cannot be recovered.

Keywords and Parameters

DEVICE TYPE deviceSpecifier	Specifies the device type for the backup used in the block recovery. See Also: "deviceSpecifier"
bmrBlockSpec	Specifies the data blocks that require recovery.
	DATAFILE datafileSpec	Specifies a list of one or more datafiles that contain blocks requiring media 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.
	CORRUPTION LIST	Recovers all blocks listed in the V$BACKUP_CORRUPTION and V$COPY_CORRUPTION views. This view is populated by BACKUP (with or without the VALIDATE option), VALIDATE, and COPY. Two types of corruption result in rows added to these views: Physical corruption (sometimes called media corruption). Oracle 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.
bmrOption	Specifies various restore options relating to the block recovery.
	FROM BACKUPSET	indicates that only backup set should be restored.
	FROM DATAFILECOPY	indicates that only datafile image copies should be restored.
	FROM TAG = 'tag_name'	indicates that only the backup set with the specified tag should be restored.
	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 7 BLOCK 5, 98, 99 DATAFILE 9 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 set 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 and forces the blocks to be restored from backups created at least two days ago:

BLOCKRECOVER TABLESPACE SYSTEM DBA 4194404, 4194405 RESTORE UNTIL TIME 'SYSDATE-2';