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Re: Question about Archivemode

From: Howard J. Rogers <>
Date: Thu, 18 Jul 2002 08:34:25 +1000
Message-ID: <ah4rcd$en2$>

"Howard J. Rogers" <> wrote in message news:ah4r3k$ecu$
> "Ryan" <> wrote in message
> news:R4lZ8.92701$
> > Ok this is a really basic Backup and Recovery question.
> >
> > If someone drops the system tablespace, ie, an intruder.
> >
> > Is it possible to perform a backup from the redo logs
> I'll stop you right there, and say that the question as posed doesn't make
> sense. You don't backup anything 'from' the redo logs. You use redo logs
> recover a copy (ie, a backup) of a datafile.
> >in you are not in
> > archive mode or have any software like RMAN installed? Or do I have to
> > recover from my last cold backup?
> >
> The rules are exactly the same, whatever tablespace you are talking about
> (with the exception of temporary tablespaces). SYSTEM is no different from
> DATA or TOOLS in this respect. Either you can apply an uninterrupted
> of redo from the time a backup of the datafile was taken to the time the
> rest of the database is at, or you can't.
> If you're not in archivelog mode, then the chances of you being able to
> supply such an uninterrupted redo stream is vanishingly small. Therefore,
> you won't be able to bring the backed-up datafile into synch. with the
> of the database, and therefore the database can't be made to function
> properly.
> How then do you get the database consistent and useable? By restoring the
> entire database from your last cold backup, as you say.
> There is one scenario where, despite not being in archivelog mode, you
> get away with a complete and perfect recovery: if the continuous stream of
> redo you require still happens to be sitting in the online logs. If you
> 5 online redo log groups, which switch every half hour, then you have 2.5
> hours of redo available to you. So if you backed up last night, opened the
> database at 9.00am, and the intruder swiped the system tablespace at
> 11.00am, you're doomed.

BONG! I meant to say 12.00 noon.... you've 2.5 hours of redo available, and he swipes it three hours after the database is opened... *then* you're doomed. 11.00am would be OK, because (despite my pathetic maths) that's only 2 hours after being opened for business, so the required redo should still be available.

Sorry. (Walks away muttering to himself.... "9+3=12, not 11", "9+3=12, not 11")

>But if he swiped it at 9.45am, the redo required to
> recover the backup of the system datafile is still available in the online
> logs, so you could just restore that one file and do a recovery on it.
> Clearly, there's no guarantees, though, that the required redo would be
> available. Only archivelog mode can make that guarantee.
> Regards
> > For those of you who saw an earlier post of mine... no this did not
> happen.
> > :)
> >
> >
Received on Wed Jul 17 2002 - 17:34:25 CDT

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