Re: why do you apply undo before redo?

From: Wayne Warren <>
Date: Mon, 19 Apr 2004 17:24:06 GMT
Message-ID: <WWTgc.85993$>

I'm not sure that the book is correct. I wrote a transaction processing system (released on 1993 as Velocis Database Server, now called Birdstep RDM Server) which performs redo operations just prior to undo operations. I can assure you that in practice it works.

If transactions have maintained proper Isolation (the "I" in ACID) from one another, then the order of redo/undo should be irrelevant. Implementation specifics may dictate the order, but the transaction recovery concept does not.

"Ryan" <> wrote in message news:_Ulgc.4499$uF3.1441_at_lakeread04...
> I'm reading a generic database textbook and it states that when databases
> are recovering undo is applied before redo. It doesn't say why. Does
> know?
Received on Mon Apr 19 2004 - 19:24:06 CEST

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