On Sun, 2004-11-07 at 11:15, Joachim Wieland wrote:
> On Sat, Nov 06, 2004 at 07:17:29PM +0000, Simon Riggs wrote:
> > > > Once you have brought up a database in timeline N+1, you can't use it as
> > > > the base to recover to a point in timeline N because the data file
> > > > contents cannot be trusted to be identical to the way they were in
> > > > timeline N.
>
> > > You mean "in timeline N ... to a point in timeline N+1", don't you?
>
> > Specifically not. The point is: you can't go back in time. Recovery is a
> > rollforward operation, so you must start at an earlier point and
> > rollforwards from there.
>
> Ok, that seems to be pretty intuitive. But could one extend the recovery
> mechanism such that one can go from PIT t_0 to PIT t_1 with t_1 > t_0
> without re-restoring the original backup?
>
Same question, just restated.
When you stop recovery at point in time, t_0 is now in timeline N+1,
though it does also still exist in timeline N. In the new timeline there
is no such thing (yet) as a time/transaction > t_0.
In timeline N only, you can go from t_0 to t_1, but not starting from
where you are now, because you are now at t_0 in timeline N+1.
That's the general case. ...and you can see why Tom described it as like
science fiction.
Anyway, you're trying to optimize re-recovery, which would be slightly
lower on the priority list than optimizing recovery itself.
General readers should just remember this: if you recover, and you
decide you've done it wrong, you can re-recover to a different place.
You don't need to understand all of that complexity to use the PITR
facilities.
--
Best Regards, Simon Riggs
