[rrd-developers] Update ex post?

[Thorsten von Eicken]

> So, what's the approach those tools are using (I've never looked at any
> of those [nor have I looked *for* any ;-)])?
>
> Cheers,
> Sebastian
>

Something I wrote quite a while ago is a resampling tool, that would 
construct a new RRD using data from an old one, and for each CDP looks 
into the old one to get the best data match, and interpolate or combine 
values. I used this heavily in a former life to change existing RRDs 
full of data when we changed the amount of data we stored in each RRD. I 
haven't maintained this and it's rrdtool 1.2 vintage, ca. 2005.

What I'm looking for now is the ability to splice RRDs together. The use 
case is replacing a server, for example, we replace www1 by www1-new 
and, after the fact, I'd like to splice the graphs together at the time 
we cut over service. Operating in the cloud we do this a lot. In this 
case I don't mind a discontinuity at the splice point, in fact, I would 
probably add a DS or something to mark the splice point so I can draw a 
vertical line on graphs.

The splicing could also be very useful for restoring data. E.g., if a 
monitoring server dies we can quickly replace it with a new one, but 
that doesn't have any data. So all the RRDs start out empty and record 
new data coming in. When we get the data from the failed one restored, 
we'd like to splice the old and new together.

I'm not expecting someone else to build the above and it's still a 
little out on the roadmap here. I have a bunch of other exciting stuff 
to contribute to rrdtool in the pipeline... I just wanted to chime in :-).

Cheers,
     Thorsten