Re: Online backup: Backup online redologs?

On Sun, 13 May 2001 00:04:47 +1000, "Howard J. Rogers" <howardjr_at_www.com> wrote:

>
>Worse. Suppose you manage to get a cleanish copy of the current redo log.
>Your database then blows up, because datafile 6 is corrupted. Now you tell
>Junior DBA to deal with it, because you have a major pizza to deal with.
>So he restores the lot: controlfile.bkp, datafiles.bkp and redologs.bkp.
>They were, after all, in your backup set ...and only having gone on the
>Introduction to SQL Course in Sydney, what did he know about restores??
>
>Guess what? The current redo log on the corrupted system WAS fine. It
>could have supplied important information. It's just been over-written by a
>copy taken ten hours ago. Every other log is fine (because every other log
>has been archived). But not the current log. The current log is toast, and
>has been replaced by very stale, hours old, toast. Net result: you've just
>lost committed transactions when there was absolutely no reason for you to
>have.

That's the most important point, I'd dare say. The fact that on restore, he could be throwing away the active redo log, replacing it with an old copy. Not that he'd do it, but a junior DBA or a sysadmin who wasn't aware could mess it up easy. Never underestimate the power of the newbie to stuff things up. I know, I was a newbie too.

(Still am when it comes to 9i and certain aspects of 8i. We all are. That's why it's important to stay actual and keep studying.)

Going back a few years when I was taking care of a V6 database that regularly needed recovery (don't ask!!!...), we got to the point where we'd backup the CURRENT set of redos and control files before starting the recovery, just in case we messed up the recovery steps somehow! That way we had assurance we could re-start the recovery. It's that important.

In fact, I'd go as far as to say even nowadays, *BEFORE* I started recovery on a corrupt database I'd make darn sure I had a copy "as is" of the current control file and redo logs. They are essential if the recovery messes up and you need to get into serious "dirk the daring" territory to get things back.

Cheers
Nuno Souto
nsouto_at_bigpond.net.au.nospam
http://www.users.bigpond.net.au/the_Den/index.html Received on Sat May 12 2001 - 21:27:00 CDT