When Oracle is run in ARCHIVELOG mode, the ARCH (Archiver) background process makes
a copy of each redo log file before overwriting it. These archived redo log files are usually written
to a disk device. The archived redo log files may also be written directly to a tape device, but disk
space is getting cheap enough that the additional cost of archiving to disk is offset by the time and
labor savings when a disaster recovery operation must occur.
NOTE
Most production databases, particularly those that support transactionprocessing
applications, must be run in ARCHIVELOG mode.
You can perform file system backups of a database while that database is open, provided the
database is running in ARCHIVELOG mode. An online backup involves setting each tablespace
into a backup state, backing up its datafiles, and then restoring the tablespace to its normal state.
NOTE
When using the Oracle-supplied Recovery Manager (RMAN) utility,
you do not have to manually place each tablespace into a backup
state. RMAN reads the data blocks in the same manner Oracle uses
for queries.
The database can be fully recovered from an online backup, and it can, via the archived redo
logs, be rolled forward to any point in time before the failure. When the database is then opened,
any committed transactions that were in the database at the time of the failure will have been
restored, and any uncommitted transactions will have been rolled back.
Pages:
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615