Wednesday, March 21, 2012

How RMAN Duplicates a database

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HOW RMAN DUPLICATES A DATABASE
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For backup-based duplication, the principal work of the duplication is performed by the auxiliary channels. These channels correspond to a server
session on the auxiliary instance on the destination host. For active database duplication the primary work is performed by target channels.

RMAN must perform database point-in-time recovery, even when no explicit point in time is provided for duplication. Point-in-time recovery is
required because the online redo log files in the source database are not backed up and cannot be applied to the duplicate database. The farthest
point of recovery of the duplicate database is the most recent redo log file archived by the source database.

As part of the duplicating operation, RMAN automates the following steps:

1) Creates a default server parameter file for the auxiliary instance if the following conditions are true:

    -    Duplication does not involve a standby database.

    -    Server parameter files are not being duplicated.

    -    The auxiliary instance was not started with a server parameter file.

2) Restores from backup or copies from active database the latest control file that satisfies the UNTIL clause requirements.

3) Mounts the restored or copied backup control file from the active database.

4) Uses the RMAN repository to select the backups for restoring the data files to the auxiliary instance. This step applies to backup-based
duplication.

5) Restores and copies the duplicate data files and recovers them with incremental backups and archived redo log files to a noncurrent point in time.

6) Shuts down and restarts the database instance in NOMOUNT mode.

7) Creates a new control file, which then creates and stores the new DBID in the data files.

8) Opens the duplicate database with the RESETLOGS option and creates the online redo log for the new database.

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