Last updated on SEPTEMBER 08, 2017
Applies to:Oracle Database - Enterprise Edition - Version 126.96.36.199 and later
Information in this document applies to any platform.
Rolling Forward a Physical Standby Database Using the RECOVER FROM SERVICE Command
A standby database is a transactionally-consistent copy of the production database. It enables production Oracle database to survive disasters and data corruption. If the production database becomes unavailable because of a planned or an unplanned outage, Data Guard can switch a standby database to the production role, minimizing the downtime associated with the outage. Moreover, performance of production database can be improved by offloading resource-intensive backup and reporting operations to standby systems. As you can see, it’s always desirable to have standby database synchronized with the primary database.
Prior to 12c, in order to roll forward the standby database using incremental backups you would need to:
- Create a control file for the standby database on the primary database.
- Take an incremental backup on the primary starting from the SCN# of the standby database.
- Copy the incremental backup to the standby host and catalog it with RMAN.
- Mount the standby database with newly created standby control file.
- Cancel managed recovery of the standby database and apply incremental backup to the standby database.
- Start managed recovery of standby database.
In 12c, this procedure has been dramatically simplified. Now you can use the RECOVER … FROM SERVICE command to synchronize the physical standby database with the primary database. This command does the following:
- Creates an incremental backup containing the changes to the primary database. All changes to data files on the primary database, beginning with the SCN in the standby data file header, are included in the incremental backup.
- Transfers the incremental backup over the network to the physical standby database.
- Applies the incremental backup to the physical standby database.
This results in rolling forward the standby data files to the same point-in-time as the primary. However, the standby control file still contains old SCN values which are lower than the SCN values in the standby data files. Therefore, to complete the synchronization of the physical standby database, the standby control file needs to be refreshed to update the SCN#.
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