Once the copy operation is complete, the database instance can be started.
Offline backups are similar to export backups because they are point-in-time backups and
therefore of less value if up-to-the minute recovery of the database is required and the database
is not in archivelog mode. Another downside to offline backups is the amount of downtime
necessary to perform the backup; any multinational company that needs 24/7 database access
will most likely not do offline backups very often.
Chapter 1: Getting Started with the Oracle Architecture 39
Online Backups
If a database is in archivelog mode, it is possible to do online backups of the database. The
database can be open and available to users even while the backup is in process. The procedure
for doing online backups is as easy as placing a tablespace into a backup state by using the alter
tablespace users begin backup command, backing up the datafiles in the tablespace with operating
system commands, and then taking the tablespace out of the backup state with the alter tablespace
users end backup command.
RMAN
The backup tool Recovery Manager, known more commonly as RMAN, has been around since
Oracle8. RMAN provides many advantages over other forms of backup. It can perform incremental
backups of only changed data blocks in between full database backups while the database remains
online throughout the backup.
RMAN keeps track of the backups via one of two methods: through the control file of the
database being backed up, or through a recovery catalog stored in another database.
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