Re: how is v$backup populated in mount stage?

"John Hurley" <johnbhurley_at_sbcglobal.net> wrote in message news:d4d6f278.0411040329.9686b8f_at_posting.google.com...
>> Scenario: instance is in mount stage using a control file that was
>> either copied (rman) when database had no tablespaces or all
>> tablespaces in backup mode.
>>
>> Queries against v$backup always return correct status (ACTIVE or
>> opposite) even when control files are switched back and forth.
>>
>> It sure seems like the query is tacking a peek at the header of each
>> datafile and getting the backup status from there instead of from the
>> control file (where I was expecting it to be from ... aka potentially
>> incorrect).
>>
>> Not complaining -- the info being returned is correct. Probably just
>> my understanding of mount stage needs refining.
>>
>> Under what conditions/circumstances does oracle in mount stage
>> actually look at datafiles?
>
> Anyone? I can post examples and test cases and will eventually but
> thought some of the gang here might already have an answer.

It's obvious that the information about whether something is in hot backup mode or not is stored within the data files themselves. If it were otherwise, then crashing your instance in the middle of a hot backup would not result in 'file 6 needs media recovery' errors, because having noticed file 6's checkpoint change number was out of synch, the control file would have been able to say 'but don't worry about it, because I know that file is in hot backup mode'.

The fact is, you *do* get such error messages, therefore the control file cannot be the source of information about whether something is in hot backup mode or not.

Since no-one these days should be doing O/S-style backups, however, the issue is akin to worrying about angelic hosts, terpsichore, and small sharp metal objects.

HJR Received on Thu Nov 04 2004 - 09:15:18 CST