Re: a practice question of backup & recovery

It's terrible questions like this that should be eliminated from the test... not because they're hard or "tricky," but because they are poorly worded, do not actually test knowledge on the subject (more on just your ability to decipher the question or guess what they're driving at), and are not in touch with the realities of DBA work.

If my control files are gone or corrupt, isn't the database down? So what does answer C have to do with anything?? Unless the instance is able to continue running without the control files (what happens if a CKPT occurs?), I'm not sure what this answer even means.

Answer A is not related to the control file restoration and requires some assumption that recovery may involve restoring the datafiles. Yes, if I need datafiles restored, I'd probably worry about fixing the control file after restoring my datafiles, but answer A is a poor one.

Answer B is too broad a statement. Yes, somewhere between restoring files (like the control file) from backup and applying redo logs during the database recovery, the control file must be recreated. Well, duh.

Answer D is the only statement that really even involves rebuilding the control file... and in most circumstances where the control file (and it's mirrored copies) are all destroyed, this step is most certainly going to be necessary.

So, according to this "tricky" question, I got it all wrong. Bleh. Someone please set me straight.

In article <ebgImgjNBHA.300_at_net037s.hetnet.nl>, "Anton Buijs" <aammbuijs_at_hetnet.nl> wrote:
>The question does not mention a clone situation so I can't take that into
>consideration for the answer.
>
>That creating the controlfile has to be the first step in a recovery process
>in clear: without a controlfile no mounted database.
>So: answer A is impossible.
>
>As far as my knowledge goes (with 10 years Oracle DBA experience, just
>passed for the Oracle 8 Backup and recovery OCP exam):
>1. To be able to create a new controlfile ('alter database backup
>controlfile to trace (or to <file>) the db must be mounted or open. (Test on
>a nomounted db gives ORA-1507).
>2. If I can create a new controlfile from a mounted or open database this
>implies the current controlfile is valid, so why would I need a new
>controlfile?
>3. If I need a new controlfile this implies the current ones are all damaged
>or lost so I can't mount the db anymore and therefore I can't make it from
>the db anymore.
>So: answer C is impossible. Apparently I must be overlooking something here.
>
>Anser D assumes I have a backup controlfile made before this situation
>occured (to trace or to file, does not matter). So it is possible but
>requires an assumption.
>
>But answer B is also possible: before the tapes are restored I have a lot of
>time to manually type in a script that does a 'create controlfile ......' .
>After using it I can apply the redo logs (assuming archived redo logs and
>the database is running in archive log mode)
>
>When I check the book (A76993-01 Backup and Recovery Guide Release 2
>(8.1.6), Chapter 6 - Media Recovery Scenario's, Loosing all copies of the
>current controlfile) the only way to recover is using a 'backup controlfile
>to file' file, create an new one using the (if necessary adjusted) statement
>from 'backup control file to trace' file or manually type in the create
>controlfile statement again - which is almost impossible because I must know
>the filename's belonging to the file id's (that is: in the order the
>datafiles where added to the database).
>
>I don't say the OCP exams should be easy. A difficult exam make the
>"Certified DBA" certificate more valuable.
>But it are these kind of questions that makes it nasty.
>
>Anton Buijs
>
>Reid Lai <reidlai_at_netvigator.com> schreef in berichtnieuws
>3B965D91.D009C355_at_netvigator.com...
>> How about your control file was corrupted? Or you need to do physical
>> cloning?
>>
>> Cheers,
>>
>> Reid Lai
>>
>> Dino Hsu wrote:
>>
>> > Dear all,
>> >
>> > A practice question:
>> > If the DBA must re-create the control file as part of database
>> > recovery, in which of the following ways should it be done?
>> > A. After backup datafile restoration
>> > B. Between restoring backups and applying redo logs
>> > C. Before closing the database to user access
>> > D. Using the script containing the create controlfile command in the
>> > trace directory
>> >
>> > The answer is C,
>> > Explanation: This question is tricky, and requires careful reading of
>> > the question as well as thorough knowldege of the Oracle database
>> > recovery process. Creation of a control file for the database recovery
>> > process should be accomplished first. The other choices are all
>> > incorrect becasue they place the creation of control files later in
>> > the recovery process.
>> >
>> > I cannot remember any scenario that requires creating a copy of
>> > controlfile first although there are some which do recovery when
>> > controlfiles are missing or damaged. Your comments are highly
>> > appreciated.
>> >
>> > Dino
>>
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Received on Wed Sep 05 2001 - 14:40:48 CDT