This capability allows round-the-clock database availability to be achieved
while still guaranteeing the recoverability of the database.
Although online backups can be performed during normal working hours, they should be
scheduled for the times of the least user activity for several reasons. First, the online backups will
use operating system commands to back up the physical files, and these commands will use the
available I/O resources in the system (impacting the system performance for interactive users).
Second, while the tablespaces are being backed up, the manner in which transactions are written
to the archived redo log files changes. When you put a tablespace in ???online backup??? mode, the
DBWR process writes all the blocks in the buffer cache that belong to any file that is part of the
tablespace back to disk. When the blocks are read back into memory and then changed, they will
be copied to the log buffer the first time that a change is made to them. As long as they stay in the
buffer cache, they will not be recopied to the online redo log file. This will use a great deal more
space in the archived redo log file destination directory.
NOTE
You can create a command file to perform your online backups,
but using RMAN is preferred for several reasons: RMAN maintains
a catalog of your backups, allows you to manage your backup
repository, and allows you to perform incremental backups of the
database.
Follow these steps to perform an online database backup or individual tablespace backups:
1.
Pages:
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645