RE: Fav. Urban Legend...

How about a datafile is lost before it is backed up during the hot backup. Where will you restore the file from? *You cannot use the backup from before; the logs have been reset. You could, however, use a cold backup. Once the hot backup is finished the cold one is not needed, but until then you are vulnerable.

• I suppose one could get the transactions from logminer, go back to this backup, reset the logs and then apply the transactions. I wonder if that's been tested.

Ian MacGregor
Stanford Linear Accelerator Center
ian_at_slac.stanford.edu

-----Original Message-----
Sent: Friday, March 15, 2002 4:28 PM
To: Multiple recipients of list ORACLE-L

Hi Jared,

> > * You *have* to take a COLD backup of the database after using
> resetlogs.
> > (Not required - a Hot backup and archive logs is adequate. All hot
> backups /
> > archive logs prior to that are invalid, though...)
>
> Consider the following:
>
> Time:
>
> t0: database restored
> t1: database opened with RESETLOGS
> t2: hot backup started ( database in archive log mode )
> t3: users input very important transactions
> t4: database crashes, and must be restored
>
> How will you recover the transactions from time t3?

As long as the online redologs are available, this should be no problem. I have successfully recovered databases where a log switch did not occur and recovery had to use an online redo log. (I am assuming that the lost datafiles will be restored from this hot backup fresh off the tapes)

On the other hand, if the online redolog is hosed you have lost the transactions anyway, _regardless_ of the fact that a Cold backup was taken. Then you will have to go back to the _previous_ incarnation and redo the restore and then perform a ccf/resetlogs (i.e. back to square one). If you have a Cold backup, you restore the cold backup and go on with life. I.e. in both cases (availability of cold or hot backup, lost online redo log), you have lost transactions...

Additionally, with a Hot backup and depending on what was lost, you can at least perform tablespace/datafile recovery . With a cold backup, you will have to restore the whole database....

The point I was trying to make was that a Cold backup after a RESETLOGS does not serve anything. Maybe there is still a gotcha I have not been able to figure out, so Backup/restore Gurus: take a bash at this logic! I would love to be corrected.

(Btw, the previous recovery scenario was on 7.3.4 - things could have changed since, and I have not been able to test that out...)

John Kanagaraj
Oracle Applications DBA
DBSoft Inc
(W): 408-970-7002

Grace - Getting something we don't deserve Mercy - NOT getting something we deserve

Click on 'http://www.needhim.org' for Grace and Mercy that is freely available!

• The opinions and statements above are entirely my own and not those of my employer or clients **

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