Re: why do you apply undo before redo?
Date: Sun, 18 Apr 2004 13:21:19 -0400
"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message
> Ryan wrote:
> > I'm reading a generic database textbook and it states that when
> > are recovering undo is applied before redo.
> Any specific reason why you would like the title of the book to remain a
> secret? :-)
I didn't want to type it. Its 'Database Systems Concepts'. The one used everywhere.
> > It doesn't say why. Does anyone know?
> Because some of the operations of the transactions of the UNDO list
> might conflict with those in the REDO list. So if you did the undo-phase
> last you might be erasing the result of some operations that you first
> did in the redo-phase.
don't quite get this. Oracle applies redo, then rollsback all open
transactions? This is why that statement intrigued me since one database
system does it the opposite way.
> -- Jan Hidders
Received on Sun Apr 18 2004 - 19:21:19 CEST