Re: why does oracle recovery redo before undo?
- From: "Ryan" <ryan.gaffuri@xxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 19 Apr 2004 18:38:26 -0400
that is what i thought. I have a generic database book that is used at most
universities that says its optimal to apply undo before redo. trying to
figure out where it is coming from.
----- Original Message -----
From: "Mladen Gogala" <mgogala@xxxxxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Monday, April 19, 2004 6:09 PM
Subject: Re: why does oracle recovery redo before undo?
>
> On 04/19/2004 05:28:27 PM, Ryan wrote:
>
> > Now my book says the optimal way to do this is to check for all open
transactions at the time of the last checkpoint that have committed after
that checkpoint.
> >
> > Anyone know more? In particularly know 'why'?
>
> It's elementary, my dear Ryan. Oracle has first to recover transactions
> to roll them back. If the changes recorded in the undo blocks are not
> applied to the database, how do you propose to roll them back?
> --
> Mladen Gogala
> Oracle DBA
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