Re: Redo for the Undo

  • From: Lothar Flatz <l.flatz@xxxxxxxxxx>
  • To: gogala.mladen@xxxxxxxxx, oracle-l@xxxxxxxxxxxxx
  • Date: Fri, 15 Dec 2023 09:03:41 +0100

Hi Mladen,

thanks. Got that. Having a hard time to figure why this would be needed.
I guess after a database crash when you restore a backup the before images prior to the restore point might be missing. Therefore roll forward will reinstall them in order to be able to cope this flash back.
Other than that I see no reason for it since roll forward will generate the related undo anew.

Or, probably more generally speaking, restore should reconstruct the database state in its whole, not leaving out parts (like undo).

Thanks

Lothar



Am 13.12.2023 um 15:34 schrieb Mladen Gogala:

On 12/13/23 07:53, Lothar Flatz wrote:
Hi,

can a conventional delete produce redo for undo? And why? What I don't get: if the redo is applied, undo would be generated anyway, would it not?

But maybe my idea of roll forward is a bit simplistic. Not really my area of expertise.

Thanks

Lothar

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Hi Lothar,

Delete changes blocks, UNDO blocks among other things.  REDO mechanism protects the UNDO tablespace as well and generally writes any block change to the UNDO tablespace.

Regards

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Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com

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