Re: Online backup: Backup online redologs?

So now it's hot backups of controlfiles you're worried about? (I wish you'd make up your mind!)

If you have 3 controlfiles, and lose 2 of them, you can simply copy the remaining one into the locations still referenced by the init.ora.

But if you lose all 3, then you have two options. You can restore binary versions of the controlfile taken during a previous backup, or you can run the
controlfile trace script.

The problem with using the binary image is that the SCN number it contains will
be *behind* the SCN stored in the datafiles. That is not an insuperable problem, because you warn Oracle that that is the case with the 'using backup
controlfile' clause... but you still won't be able to open the database, unless
you issue a resetlogs -and a resetlogs renders all prior backups and archives
effectively useless, so your database is left in a very vulnerable state.

For that reason, the use of the trace file is the *recommended* way of restoring
all controlfiles, becaue it cheats... containing the paths to all the datafiles,
Oracle knows where to look for them. It then finds the highest SCN of any datafile, and uses that as the SCN to write into the header of the new Controlfiles. Net result: the controlfiles are re-constructed, with an SCN that
means that a resetlogs is not required. It's a much 'cheaper' way of performing
the recovery, and all prior backups and archives are still useable.

In fact, the binary backup and the trace backup should both be employed, because
the binary version does have a specific use: to recover from the dropping of an
entire tablespace, for example -ie, in those situations where the existing controlfiles no longer describe the physical and logical structure of the database you wish to recover.

So there is a use for both, but the trace file is definitely the option of first
resort.

HJR
[Snip]

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The views expressed are my own only, and definitely NOT those of Oracle
Corporation


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