About Oracle Database Incarnations  

Posted by Mawahid


 Whenever you open the database with the command ALTER DATABASE OPEN RESETLOGS , a new incarnation is created. Performing an OPEN RESETLOGS do the following,

-Archives the current online redo logs,

-Incarnation resets the log sequence number to 1, and then

-Gives the online redo logs a new time stamp and SCN.

-Increments the incarnation number, which is used to uniquely tag and identify a stream of redo.

Parent, Ancestor and Sibling Database Incarnations
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•The incarnation from which the current incarnation branched following an OPEN RESETLOGS operation is called the parent incarnation of the current incarnation.

•The parent incarnation and all of its parent incarnations are the ancestor incarnations of the current incarnation.

•Two incarnations that share a common ancestor are sibling incarnations if neither one is an ancestor of the other.

•To view the incarnation history of a database use the RMAN>LIST INCARNATION; commnad.

•By default, when used command like FLASHBACK DATABASE or RECOVER... UNTIL, an SCN is assumed to refer to the current incarnation path, rather than sibling incarnations.

•However, you can use the RESET DATABASE TO INCARNATION command to specify that SCNs are to be interpreted in the frame of reference of another incarnation.

•For example my current database INCARNATION is 5 and now I have used
FLASHBACK DATABASE TO SCN 6666;
then SCN 6666 will be search in current incarnation which is 5. However if I want to get back to SCN 6666 of INCARNATION 4 then I have to use,

RMAN> RESET DATABASE TO INCARNATION 4;
RMAN> RECOVER DATABASE TO SCN 6666;


•When a database goes through multiple incarnations, some backups can become orphaned. Orphaned backups are backups that are created during incarnations of the database that are not ancestors of the current incarnation.

•For example, database incarnation is 5 and SCN is 7000. A DBPITR is done at SCN 7000 to SCN 6666 and then RESETLOGS is performed. Now in current incarnation 6 the backup taken between 6666 and 7000 SCN became orphaned.

•Orphaned backups are usable by RMAN in cases where you wish to restore the database to a point in time not in the current incarnation path.

This entry was posted on Tuesday, January 11, 2011 at 6:22 AM . You can follow any responses to this entry through the comments feed .

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