ora file or server parameter file (SPFILE)
CAUTION
You should never, ever, want or need to back up online redo log files.
Although there is a slight time-savings for restoring from a cold backup
after a clean shutdown, the risk of losing committed transactions
outweighs the convenience. Your online redo logs should be mirrored
and multiplexed so that you (virtually) never will lose the current
online log file.
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394 Oracle Database 11g DBA Handbook
Having all these files backed up while the database is closed provides a complete image of
the database as it existed at the time it was closed. The full set of these files could be retrieved
from the backups at a later date, and the database would be able to function. It is not valid to
perform a file system backup of the database while it is open unless an online backup is being
performed. Offline backups that occur following database aborts will also be considered
inconsistent and may require more effort to use during recoveries if they are usable.
Online Backups
You can use online backups for any database that is running in ARCHIVELOG mode. In this
mode, the online redo logs are archived, creating a log of all transactions within the database.
Oracle writes to the online redo log files in a cyclical fashion: After filling the first log file, it
begins writing to the second, until that one fills, and then it begins writing to the third. Once the
last online redo log file is filled, the LGWR (Log Writer) background process begins to overwrite
the contents of the first redo log file.
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