Re: Online backup: Backup online redologs?

"Charles Fisher" <charles.fisher_at_alcoa.com> wrote in message news:3AEDB746.2050104_at_alcoa.com...
> Howard J. Rogers wrote:
>
> >>> See above. It makes no sense to backup the online redo logs. They've
> >>> already all been backed up to the archives, with the exception of the
> >>> current log. If you are that concerned, then a switch log file will
> >>> cause
> >>> that to be archived, and by backing up that last archive, you've got
 the
> >>> lot.
>
> EXCEPT that you cannot execute the output of 'ALTER DATABASE
> BACKUP CONTROLFILE TO TRACE' without the presence of the
> redolog files, one of which must be marked as active.
>

You shouldn't take a reply to one person's query out of context. That reply was referring to a worry about not having the very last transactions in a given hot backup, and had nothing to do with cloning a database.

> What is really the difference between a restore with a hot
> copy of the redo and a recovery of a crashed instance which
> corrupts a number of tablespaces?

The difference is that corrupt tablespaces can be replaced with inconsistent versions, and brought into a state of consistency by the application of redo. Restoring hot copies of redo logs means you are restoring inconsistent files which can NOT be mad consistent by any means.

>Wouldn't each situation
> introduce the same sort of corruption?
>

Yes, sort of. Both sorts of files will be internally inconsistent (corrupt, if you prefer). Corruption is corruption is corruption. It's what you can *do* about the corruption that makes the difference, and there's sod-all you can do about corruption in redo logs.

> It would make much more sense if there were an option to the
> CREATE CONTROLFILE statement to create blank redologs. Oracle
> should struggle to make this easy; this ambiguity is not useful.

Where's the ambiguity? "You cannot take hot copies of redo logs" is pretty unambiguous. And "mirroring (or multiplexing iof you prefer) was invented precisely so that you would never be in a position of losing all members of a redo log group" is likewise fairly clear-cut.

>
> I don't understand why people are so evasive on this issue.

I don't understand why certain people can't simply approach this issue with logic and clarity, instead of seeking to do the impossible by utterly illogical means.

Regards
HJR Received on Mon Apr 30 2001 - 19:47:36 CDT