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Never is a long time.
While I agree with the generalization, if one is testing, and it might make sense to back everything up, including the online redo logs (assuming db is closed), so that later restores bring the db back to the exact same state.
You'll want those backed up during a migration as well, unless logs have been switched and archived.
Admittedly, these are very specialized and specific cases. I'd hate to see someone backup the online logs and then restore the db, with those log files, and lose data. That is the real danger.
This is also one reason why some suggest online logs on raw - just to have another way to point out how special and different these files are.
There's probably no documentation that "says to include online redo logs as part of a backup".
However, there are situations where you can (or even would want to) include your
redo logs in a backup. Note that I say "a backup", not "backups". A specific, adhoc,
backup may include redo logs.
1. I take a cold backup of a database and restore it to another server. I do not wish to do a RESETLOGS (why, I ask "do I HAVE to resetlogs ?"). Then, I include my redo logs in my cold backup and restore.
2. I am testing backup and recovery scenarios. I take a cold backup of the whole database as a "reference point" in all my various recovery tests.
3. I am attempting a recovery of a production database to verify data at different points in time. I know that I might have to also do a resetlogs in between, change the
incarnation id, maybe even change the db_name etc. I want to be able to revert to
any restored image during the few rounds of restore-and-verify-data. Those
intermediate backups would well be cold backups with redo logs (after resetlogs ?)
4. I am remotely advising a DBA on recovery of a crashed database. I cannot be
sure that he has verified all the archivelogs, got the current log sequence numbers etc.
I know that it is likely that one or more of the online redo logs hadn't yet been archived
and I would be able to "simulate" them as archived logs during the recovery -- but only
if I do ensure that the redo logs are backed up.
5. The last one or two archivelogs had not got included in the tape backup. However,
since I know that the database has 4 or 5 or 6 online redo logs, those last two are
still available "on-disk" in the form of "online" redo logs (which might very well be
raw devices, just to make things more complicated), which haven't been "lost" in the
Bottom Line : As a "general" rule, it is not necessary to backup online redo logs.
As a "general" piece of advise, it can be dangerous to blindly backup online redo
logs, even in cold backups.
However, there can be specific cases where I know I would want to backup the online
Remember that "online redo logs" doesn't mean exactly the same as "CURRENT"