Re: what happens if you lose a rollback segment?

On Sat, 18 Oct 2003 13:13:31 -0400, "Ryan" <rgaffuri_at_cox.net> wrote:

>yes Im AWARE of that. However, there are different types of failures. Lets
>say all your datafiles are fine, but you lose a Rollback segment during the
>day at say 1PM. You have alot of uncommitted transactions.
>
>Therefore you are forced to restore from last nights backups right? The
>rollback tablespace is from LAST NIGHT. So your rolling forward for 12
>hours, all the rollback information in your nightly backed up rollback
>tablespace is outdated by then. So why do we take backups of rollback
>tablespaces?
>
>or do you take backups of rollback tablespaces more often than datafiles
>that way if you lose one you dont have to restore from such an old copy?

You REALLY want to have to have it SPELLED OUT , don't you.

A database consists of tablespaces.
When you backup you make a consistent image. If you leave out one tablespace, you don't have a consistent image. If you don't have the rollback tablespaces: YOU WON'T BE ABLE TO ROLLBACK THE TRANSACTIONS THAT HAVE BEEN ROLLED BACK, SINCE YOU LAST BACKED UP.
*BOTH* (I SAY: B O T H) THE BEFORE AND THE AFTER IMAGE OF A TRANSACTION ARE IN THE REDO LOGS.
BOTH IMAGES CONSIST OF CHANGE VECTORS ONLY. YOU CAN'T RECONSTRUCT THE BLOCK CONTENTS WITH CHANGE VECTORS ONLY, YOU'LL NEED TO RECONSTRUCT THE ROLLBACK BLOCK, TO BE CAPABLE TO ROLL BACK. YOU CAN'T ROLL BACK BECAUSE SOMEONE IN YOUR ORG (YOU) DECIDED NOT TO BACKUP THE ROLL BACK TABLESPACE. THAT WAS THE END OF YOUR DATABASE. I YOU REALLY DON'T WANT TO BUY MY ANSWERS, TRY IT FOR YOURSELF, AND STOP NAGGING ME BY REPEATING OVER AND OVER AGAIN THE SAME HOGWASH. YOU DON'T UNDERSTAND WHAT TRANSACTIONS ARE AND YOU DON'T UNDERSTAND WHAT ROLLBACK IS.

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Sybrand Bakker, Senior Oracle DBA