Re: why do you apply undo before redo?

From: Wayne Warren <wwarren_at_MANGLEbirdstep.com>
Date: Mon, 19 Apr 2004 17:24:06 GMT
Message-ID: <WWTgc.85993$vn.249185@sea-read.news.verio.net>

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" <rgaffuri_at_cox.net> 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
anyone
> know?
>
>
Received on Mon Apr 19 2004 - 12:24:06 CDT