Re: Which backup file?

On Thu, 07 Aug 2003 00:32:06 GMT, Cory Brooks <coryb_at_nc.rr.com> wrote:

> If I'm using rman and have a backup that starts at 7 and ends at 8 and
> need
> to do a point in time recovery to 7:45, a point in time when some but not
> all files in the DB will have been copied onto the backup medium.
> Clearly
> for those files which have not yet been copied, Oracle would need to go
> back
> to the previous backup and roll forward. My question is for those files
> that have been completely copied in the latest backup, that is, those
> files
> copied before 7:45, do Oracle and rman communicate to use the newer
> backup
> of the files that were copied before 7:45 to reduce the amount of changes
> that must be applied from the logs?
>
> Oracle would still have to read through all logs from the earlier backup
> for
> those files that have not been copied. I'm wondering if there is a
> benefit
> to reducing the amount of changes to be applied.
>
> Thanks,
> Cory
>
>

Difficult to know with absolute certainty, but I am fairly sure it *will* use the newer files where possible. It definitely has optimisation for that sort of thing: it prefers, for example, to use disk backups rather than tape ones (other things being equal) because disks are usually faster than tapes. It prefers to use diskfile copies rather than diskfile backups, because copies just need to be restored, not pieced together and reconstructed. So, it wouldn't surprise me if some sort of optimisation as you suggest is also involved.

The way to test it, of course, is to delete one of the newer backup files before attempting the restore, and don't tell RMAN you've done it... and then see what happens. If it chugs on without complaining, it's not attempting to use the newer backup, and if it throws an error, it is.

On second thoughts, maybe a rename of the file would be a bit safer than a delete!

~QM Received on Thu Aug 07 2003 - 04:53:27 CDT