Re: Control file recovery

On 5 Sep 2005 05:59:06 -0700, "Pradeep" <agarwalp_at_eeism.com> wrote:

>>>Did you actually read my reply? Probably not, or you simply don't
>>>understand it.
>>>I was talking about controlfile, datafile and online redologs being
>>>*NOT IN SYNC* with respect to administrative data!
>
>>>And if online redologs are not available during open they are
>>>recreated automatically, albeit with incorrect administratieve
>>>information.
>
>Sybrand,
>
>Sorry, but i am still not clear. What i have understood is that the log
>sequence number and SCN number might not be same in redo logs and in
>the backup control file. but i am still not able to understand what
>happens after RESETLOGS. Does the data which is there in the Online
>logs are lost ??? What happens to the data in Datafiles ??
> I know this might be annoying you, but i'll really appreciate if you
>can try to explain in simple.

using a backup controlfile means during recovery the information in the controlfile is disregarded. The result is you can recover to anywhere, you can specify the online redologs when prompted (as was already explained in the documentation). The recovery command will prompt you for every individual archived redolog file. At a certain point there is a moment the archive simply doesn't exist *yet*, because that sequence# is the current redo log. So you specify the name of an online redolog (You might specifying the wrong redolog here, but the recover command will continue to prompt you, it will not bail out).
 If you don't have all the online redologs you simply type CANCEL when prompted.
AFTER RECOVERY you open the database with RESETLOGS. During RESETLOGS the log sequence number is simply reset to 1, it is stored in the controlfiles, the online redologs *AND* the datafiles, and all the online redologs are ready to become overwritten. So: what is recovered from the online redologs (if you still have them) is largely up to you. If you don't have them, you will loose all *transactions* in those redologs.
Basically a RESETLOGS is a 'Stunde NULL' for the database. (Stunde NULL stands for 8 may 1945, the day Nazi-Germany surrendered to the Allies). You can't go back before RESETLOGS.

--
Sybrand Bakker, Senior Oracle DBA