Databases Reference
In-Depth Information
Chapter 15
Duplicating Databases and
Transporting Data
Oracle DBAs routinely create duplicate databases by using source database backup files or by using
active
database duplication
, which lets you duplicate a database without any backups of the source database. Duplicate
databases help you test database upgrades and application changes and serve as reporting databases under some
circumstances. Duplicating a database comes in handy when you need to test a backup and recovery strategy. You
can duplicate a database when you accidentally lose a very large table and must recover it from a backup. Instead
of performing a time-consuming database recovery, you can simply create a duplicate database and export the
table and then import it into the production database. Starting with Oracle 12c, you can run the RMAN command
recover table
to restore a table to a point in time in the past by restoring the table from an rMAN backup. However,
duplicating a database may be the best solution when dealing with earlier releases.
Besides duplicating databases, RMAN's duplicate database capability also helps you set up
standby databases
,
which are not merely one-time copies of the production databases but are continually updated versions of the
production database. The primary purpose of a standby database is to serve as the production server during recovery
and failover situations. You can't use a duplicate database to perform a standby recovery and failover.
Although you can duplicate databases without using RMAN, there are several advantages to duplicating a
database with the help of RMAN:
•
You can duplicate a database without even making a backup of the source database by using
network-enabled duplication, also called active database duplication.
•
You can register a duplicated database in the same recovery catalog as the primary database,
since the duplicate database will have its own unique DBID.
•
You can exclude certain tablespaces, such as read-only tablespaces.
•
You can duplicate the database on the same server or on a remote host.
•
You also have the option, if you want, of duplicating a database to a past point in time.
duplicate
command assigns the duplicate
database a different DBID (except in cases where you duplicate a database for use as a standby
database) so you don't have to change the DBID manually with the DBNEWID utility.
•
When you duplicate a database with RMAN, the
Any database duplication you make with the help of RMAN backups is called
backup-based duplication
. Prior
to the Oracle Database 11g release, this was your only means of duplicating a database with RMAN. Backup-based
database duplication requires a source database and a backup copy of that source database, either on the source
host or on tape. Once you back up the source database, you need to transfer these source database backups to the
destination server to create a duplicate database.
