Re: Backing Up Rollback Tablespaces (Answer)

In article <1993Dec2.154908.5958_at_lmpsbbs.comm.mot.com> cds016_at_isadmin1.comm.mot.com (David Schmitt) writes:
>In article <CHD3A9.4K8_at_trc.amoco.com>, David Crowson <zdxc0d_at_amoco.com> wrote:
>>
>>With Hot backups you have to backup ALL .dbf files,control files and redo
>>logs. If you don't you will not be able to recover the database.
>
>Actually, with Oracle V6 (I don't know about Oracle 7), you don't need the
>online redo logs. You _do_ need some of the archived redo logs (the logs that
>were online during the backups) however.

Ok after more tests than my employeer would want to know about.

You can skip backing up the RBSegs ONLY if you know that each transaction was allowed to rollback any uncommited updates/deletes/inserts prior to the crash that caused you to want to reload your backup.

Why, because if they where not, the you still have to rollback after you apply the logs, BUT you won't have anyplace to write the rollback information. This wouldn't be a big deal if you wanted all your transactions to be commited after the crash, but if you don't...

Page 15-8 of the V6 DBA guide states: "Because rollback segments are contained within the database, they are protected against media failure by the redo log, and are recovered during the roll forward process".

So as your are applying the logfiles the data tablespace AND the rollback tablespace are being updated. If you don't have them in place it will not be able to back out uncommited changes when you are done restoring the system.

The only case where you don't need the RBSegs is during a cold backup when the system was brought down with a shutdown immediate or normal.

Actually, this could be a good thing if you had a TON of uncommitted data during a crash. You could deprive it of the RBSegs and keep it from rolling back. I don't think I would want to try this on a Payroll system though. :-}

The truely amusing part is that if you bring up the database without a rollback. Then any data that should be rolled back will not be put back to its original state AND the database will never tell you anything is wrong.

Ouch. The least I expected was a warning that I was really messing up.

-- 
Regards, 

Lee E. Parsons                  		Baker Hughes Inteq, Inc
Oracle Database Administrator 			lparsons_at_exlog.com