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Re: why do you apply undo before redo?

From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Sun, 18 Apr 2004 12:25:12 GMT
Message-ID: <Isugc.75959$VI4.5039222@phobos.telenet-ops.be>


Ryan wrote:
> I'm reading a generic database textbook and it states that when databases
> are recovering undo is applied before redo.

Any specific reason why you would like the title of the book to remain a secret? :-)

> 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.

Received on Sun Apr 18 2004 - 07:25:12 CDT

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