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From Øystein Grøvlen <Oystein.Grov...@Sun.COM>
Subject Re: Question about undoLWM!!!
Date Mon, 03 Apr 2006 06:34:40 GMT
Raymond Raymond wrote:
> I am trying to implement incremental checkpoint. In incrememtal checkpoint,
> we write out data when system is not very busy, and update the log control
> file periodically. When we update the log control file, we need to know the
> redoLWM, undoLWM and transactiontable. In current implementation, the
> undoLWM is tf.firstUpdateInstant() (tf is transaction factory). But in 
> incremental
> checkpoint, we will update the log control file at a point(on the log 
> stream) in
> the past. Now, I got a problem that how to get the undoLWM at a point in
> the past. I can get the loginstant at that point(redoLWM), but I have no 
> idea
> is it possible for me to get the undoLWM at a point in the past?
> 

I do not think the undoLWM needs to be for a "point in the past".  The 
undoLWM tells what log is needed to be able to undo transactions at the 
end of recovery.  You are not changing the end point for recovery since 
you will still redo all log before the current checkpoint.  Hence, I 
think you should be able to use the same undoLWM as before.

--
Øystein

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