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Lesson 3 Restoring a NOARCHIVELOG database
Objective Identify the structures required to restore a NOARCHIVELOG database.

Restoring NOARCHIVELOG database in Oracle

Imagine that some or all of the datafiles in a NOARCHIVELOG database have become corrupted due to media failure. In order to recover the database in this situation, you have no option but to restore the most recent whole closed database backup.
All of the backup files must be synchronized for the database to open. This means that all datafiles and control files must have the same log sequence number and checkpoint number, unless they are offline or part of a "read-only" tablespace. This is also called consistent whole database backup. During restore, no redo logs can be applied to the affected files.

Required data structure

When a media failure occurs, a valid closed database backup must exist in order to perform a recovery. All Oracle files must be restored,even if there is only one corrupt or lost datafile. To restore a database, the following files need to be in place for the data structure to be complete:
  1. All datafiles
  2. Control files
  3. Redo logs
  4. Parameter files
  5. Password file

Recovering parameter and password files is optional. You only need to restore these files if they are damaged.
The next lesson explains the implications for recovery when a database is running in NOARCHIVELOG mode.

Recovering a NOARCHIVELOG Database with Incremental Backups

Restoring a database running in NOARCHIVELOG mode is similar to restoring a database in ARCHIVELOG mode. The main differences are:
  1. Only consistent backups can be used in restoring a database in NOARCHIVELOG mode.
  2. Media recovery is not possible because no archived redo logs exist.
You can perform limited recovery of changes to a database running in NOARCHIVELOG mode by applying incremental backups. The incremental backups must be consistent, like all backups of a database run in NOARCHIVELOG mode, so you cannot make backups of the database when it is open.
When you are recovering a NOARCHIVELOG database, specify the NOREDO option on the RECOVER command to indicate that RMAN should not attempt to apply archived redo logs. Otherwise, RMAN returns an error.
To recover a NOARCHIVELOG database with incremental backups:
  1. After connecting to the target database and the recovery catalog, place the database in a mounted state: STARTUP FORCE MOUNT
  2. Restore and recover the database.
  3. For example, you can perform incomplete recovery with the following commands:
    RESTORE DATABASE
    FROM TAG "consistent_whole_backup";
    RECOVER DATABASE NOREDO;
    

  4. Open the database with the RESETLOGS option. For example, enter the following command:
    ALTER DATABASE OPEN RESETLOGS;
    

Restoring Database - Quiz

Click the Quiz link below to review your understanding of the required data structures for restore and recovery.
Restoring Database - Quiz