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Re: Media recovery when using an old controlfile

From: Jurjen Oskam <joskam_at_quadpro.stupendous.org>
Date: 25 Jun 2003 15:17:34 GMT
Message-Id: <slrnbfjf8d.b9l.joskam@calvin.quadpro.stupendous.org>


In article <WdhKa.1167$p8.43445_at_newsfeeds.bigpond.com>, Richard Foote wrote:

        [ excellent explanation snipped ]

> One word of warning here though is that because you didn't (I assume) put
> the tablespaces into backup mode, your copy of the database doesn't quite
> equate to a shutdown abort scenario. This is because a block as it's being
> copied could have a portion of it copied but then have DB Writer come and
> overwrite the remaining portion of the block. When this remaining portion

This is point I admittedly oversimplified in my original post. As you may have read in my previous post, the storage system prevents this situation: all I/O to the entire database is frozen, the copy is made (in the form of a mirror being split off), and then I/O continues. From the DB Writer's point of view, the copy of the entire database is made atomically.

> When you quite correctly run your recovery statement, you have stated to
> Oracle that the controlfile is not current and hence can't be used to police
> the required SCN of the *current* database. In other words you wish to
> perform an incomplete recovery and recover the controlfile as well.
> Therefore Oracle investigates the headers of the datafiles and determines
> which is the oldest, non read-only datafile as described in the control
> file. This is the point (and the redo log sequence) from which we wish to
> recover the database. Assuming that the last completed checkpoint was
> performed during the previous log switch, this means it's the current online
> redo that Oracle requires. That is, log 49428 is the current online redo log
> and as such can not possibly be archived.

That is what I understood as well.

> To recover the database, you must therefore copy the current online redo log
> across and *completely* apply all changes associated with this redo log.

The online redo logfiles were part of the copy-by-splitting-off-mirror, so those are available on the second machine. Are you saying that instead of pointing to log 49428 (which doesn't exist as an archived log yet, but only in an online redo log), I should point to /dev/rredo_log_volume? Will that work? How can I tell which online redolog volume to use? In that particular database, there are nine online redolog files. Will Bad Things(tm) happen if I try to apply the wrong online redolog?

> Make sense ?

Yes, very much so! Thank you, and thanks to everybody who takes part in this thread. It's really nice of all of you to provide such helpful and detailed explanations. I'm not a DBA, but I am responsible for backup/recovery so all this is excellent information with respect to Oracle backup and recovery.

-- 
Jurjen Oskam

PGP Key available at http://www.stupendous.org/
Received on Wed Jun 25 2003 - 10:17:34 CDT

Original text of this message

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