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Re: Online backup: Backup online redologs?

From: Howard J. Rogers <howardjr_at_www.com>
Date: Fri, 18 May 2001 19:58:34 +1000
Message-ID: <3b04f25c@news.iprimus.com.au>

"Charles Fisher" <Charles.Fisher_at_alcoa.com> wrote in message news:Pine.GSO.4.31.0105170921570.1445-100000_at_unknown...
> On Thu, 17 May 2001, Howard J. Rogers wrote:
>
> > 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.
>
> Here is what the Couchman 8i OCP Cert book has to say about the value of a
> controlfile trace:
>
> "In general, you won't need to create many new control files this way, but
> in case you do, you know how to do it. Plus, you should understand how to
> do this for the OCP exam."
>
> Notice that it does not say anything like "controlfile traces are critical
> components of a backup." It almost dismisses them as trivial.
>
> This Oracle documentation is exceptionally poor. I knew when I first read
> it that the advice was bad.
>

Worse than that, the trace file has important uses as the (or, at least, 'one of the') principal means of cloning a database, and it is also essential when re-naming a database. So to almost suggest that it is of only academic interest, or good for passing exams, is just plain daft.

>
> In a related question, can the dbverify command be used to check the
> consistency of a hot backup of a redolog?
>

No, because it is only designed to be applied to datafiles (online, or offline, or part of a datafile whether on or offline). The fact that there is a 'blocksize' parameter should alert you to this: there is no such thing as an Oracle block with the redo logs (as also attested by the fact that log_checkpoint_interval is measured in *O/S* blocks, not Oracle blocks).

I'm actually slightly gobsmacked that it worked at all, and full marks for perservereing (or however it's spelled) to find a block size that appears to do the trick -but the results will nevertheless be utterly meaningless, and I wouldn't waste your time further.

Regards
HJR
> The behavior of this utility seems a little odd; even though my
 db_block_size
> is 8192, dbv will not run on the redologs unless I use a block size of
> 1024.
>
> Here is the output of dbv on one of my hotbackup datafiles:
>
> --------------------------------------------------------------------------



> :/pkg/prdcrm/backup:root> dbv file=platinum.dbf blocksize=8192
>
> DBVERIFY: Release 7.3.4.4.0 - Production on Thu May 17 10:02:57 2001
>
> Copyright (c) Oracle Corporation 1979, 1996. All rights reserved.
>
> DBVERIFY - Verification starting : FILE = platinum.dbf
> Page 1 is marked media corrupt
> Page 2 is marked software corrupt
> Page 3 is marked software corrupt
> ...
> Page 12798 is marked media corrupt
> Page 12799 is marked media corrupt
> Page 12800 is marked media corrupt
>
>
> DBVERIFY - Verification complete
>
> Total Pages Examined : 12800
> Total Pages Processed (Data) : 0
> Total Pages Failing (Data) : 0
> Total Pages Processed (Index): 0
> Total Pages Failing (Index): 0
> Total Pages Empty : 0
> Total Pages Marked Corrupt : 12800
> Total Pages Influx : 0
> --------------------------------------------------------------------------


>
> Since this datafile can be recovered successfully, I guess that corrupt
> pages are not a problem.
>
> Here it is for the hot copy of the redolog:
>
> --------------------------------------------------------------------------


> :/pkg/prdcrm/backup:root> dbv file=redoprdcrm01.log blocksize=1024
>
> DBVERIFY: Release 7.3.4.4.0 - Production on Thu May 17 10:07:57 2001
>
> Copyright (c) Oracle Corporation 1979, 1996. All rights reserved.
>
> DBVERIFY - Verification starting : FILE = redoprdcrm01.log
> Page 1 is marked software corrupt
> Page 2 is marked software corrupt
> Page 3 is marked software corrupt
> ...
> Page 10238 is marked software corrupt
> Page 10239 is marked software corrupt
> Page 10240 is marked software corrupt
>
>
> DBVERIFY - Verification complete
>
> Total Pages Examined : 10240
> Total Pages Processed (Data) : 0
> Total Pages Failing (Data) : 0
> Total Pages Processed (Index): 0
> Total Pages Failing (Index): 0
> Total Pages Empty : 0
> Total Pages Marked Corrupt : 10240
> Total Pages Influx : 0
> --------------------------------------------------------------------------


>
> I get similar corruption errors on datafiles from a down instance.
>
> --------------------------------------------------------------------------


> Charles J. Fisher - Consultant
> Alcoa Davenport Works
> (319) 459-2512
>
Received on Fri May 18 2001 - 04:58:34 CDT

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