Use RMAN to Reset a Database

RMAN>reset database

1. What is the Incarnation Number?
   • The incarnation number represents a unique identity for a specific timeline of the database.
   • When a database undergoes RESETLOGS, a new incarnation is generated.
   • Oracle keeps track of all database incarnations in the control file and RMAN catalog.
2. When is RESETLOGS Used?
   • After incomplete recovery (point-in-time recovery).
   • After using RMAN DUPLICATE to clone a database.
   • After restoring a backup that is not part of the current incarnation.
   • When opening a newly recovered control file.
3. How to View Database Incarnations?
   • You can list all database incarnations using RMAN:
   
   

   RMAN> LIST INCARNATION OF DATABASE;
   

   
   Sample output:
   

   DB Key  Inc Key  DB Name    DB ID       STATUS      Reset SCN    Reset Time
   ------- -------  --------   ----------  ----------  ----------   ---------------
   1       2       ORCL       1234567890  CURRENT     2456789      10-JAN-2025
   1       1       ORCL       1234567890  PARENT      1000000      01-JAN-2025
   

   
   
   • The CURRENT incarnation is the active one.
   • The PARENT incarnation represents the previous timeline before a RESETLOGS operation.
4. How to Change to an Older Incarnation? To recover to an earlier incarnation (e.g., before a RESETLOGS), use:

   RMAN> RESET DATABASE TO INCARNATION ;
   

   
   Example:
   

   RMAN> RESET DATABASE TO INCARNATION 1;
   

   
   This tells RMAN to use backups from the older incarnation for recovery.
5. Performing Basic Maintenance with RESET DATABASE
   • If a reset logs operation was done mistakenly, and you need to restore a previous incarnation:
     1. Identify the required incarnation with LIST INCARNATION OF DATABASE;
     2. Reset the database to that incarnation using RESET DATABASE TO INCARNATION <ID>;
     3. Restore and recover the database from the appropriate backups.
   • If a new incarnation was created but causes restore/recovery issues, you may need to switch back to a previous incarnation.
6. Resetting the Database in Emergency Scenarios
   • When control files are lost and recreated, the database needs a RESETLOGS operation, which creates a new incarnation.
   • Before cloning a database, you may need to reset the incarnation number to use the correct backups.

• The incarnation number helps track different database timelines after RESETLOGS.
• Use LIST INCARNATION to view previous and current incarnations.
• Use RESET DATABASE TO INCARNATION <number> to recover from an earlier timeline.
• RMAN ensures backups from the correct incarnation are used for recovery.

• Reset Database to incarnation
  If you issue the list incarnations command, you will get a list of all incarnation records for your database. One incarnation will be current, the others will not. Review the table below to check if you have the following output from a list incarnation of databasecommand:
  

  DB KEY	INC KEY	DBNAME	DBID	CURR
  1	10	ORACLE	1234567890	NO
  1	100	ORACLE	1234567890	NO
  1	1000	ORACLE	1234567890	YES

  
  If it turns out that you have received any of the outputs indicated in the table, you can perform a reset command to restore the database back to version 10 by issuing the following command:
  

  RMAN>reset database to incarnation 10
  

  
  You will subsequently need to issue the appropriate restore and recover RMAN commands to recover the correct database files from incarnation 10. The following graphic demonstrates the output from resetting your client's database, (orc2), to incarnation 1119, which is also the current incarnation.
  

  

1. Enter the command to determine the RMAN-supported incarnations of your databases. Type list incarnation of database at the prompt and press enter.
2. Enter the command to reset the database ORC1, which is the database you are attached to, to its previous incarnation. Type reset database to incarnation 4 at the prompt and press enter.
3. This completes the simulation.

• Resetting the Database Incarnation in the Recovery Catalog
  You create an incarnation of the database when you open the database with the RESETLOGS option. You can access a record of the new incarnation in the V$DATABASE_INCARNATION view. If you open the database with the RESETLOGS option, then a new database incarnation record is automatically created in the recovery catalog. The database also implicitly and automatically issues a RESET DATABASE command, which specifies that this new incarnation of the database is the current incarnation. All subsequent backups and log archiving done by the target database is associated with the new database incarnation. Whenever RMAN returns the database to an SCN before the current RESETLOGS SCN, using either RESTORE and RECOVER or FLASHBACK DATABASE, the RESET DATABASE TO INCARNATION command is required. However, you do not need to execute RESET DATABASE TO INCARNATION explicitly in the following scenarios because RMAN runs the command implicitly with Flashback.
  
  1. You use FLASHBACK DATABASE to rewind the database to an SCN in the direct ancestral path (see "Database Incarnations" on page 14-6 for an explanation of the direct ancestral path).
  2. You use FLASHBACK DATABASE to rewind the database to a restore point. The following procedure explains how to reset the database incarnation when recovering through a RESETLOGS.

• To reset the recovery catalog to an older incarnation for media recovery:
  1. Determine the incarnation key of the desired database incarnation. Obtain the incarnation key value by issuing a LIST command:
     

     LIST INCARNATION OF DATABASE trgt;
     

Generate and output the tabular data which appears in the image.

SHUTDOWN IMMEDIATE
STARTUP NOMOUNT

RUN
{
SET UNTIL 'SYSDATE-45';
RESTORE CONTROLFILE; 
# only if current control file is not available
}

ALTER DATABASE MOUNT;

RESTORE DATABASE;
RECOVER DATABASE;
ALTER DATABASE OPEN RESETLOGS;