[rrd-developers] Re: Where to fix time modulo step problem?

[David Mitchell]

Tobias Oetiker wrote:
> Hi David,
> 
> Note that rrdtool will select the best coverage with a resolution
> equal of better to the one required for drawing the graph. This
> means that in smokeping context they only problem is probably that
> the graphs are drown until 'now' ... could you try adding
> 
> --end -$x
> 
> where $x is the number of seconds in one step of the appropriate
> RRA resolution for the graph ...

Ah, I didn't think to try that. I had only experimented with adjusting 
the start and end times to be even multiples of the RRA resolution. 
Simply adding something along the lines of '--end -'.($start / $width) 
into smokeping.pm had the desired effect.

> 
> in any event, a patch for rrdtool which makes the rrd_fetch
> algorithm smarter, putting a healthy balance between coverage and
> resolution match would certainly be appreciated ...

I have to admit, based on your hint the patch to smokeping to speed it 
up in my case is so simple it makes it hard to justify digging into the 
RRD code itself. Here's the tweak I made to smokeping.pm. It has the 
effect of delaying the introduction of new data into the graphs, but the 
lag is only one 'pixel' of time. But I'm happy. I now have quick-drawing 
graphs while at the same time saving 5 years of 60 second data on the 
backend. Just in case I want to do any real analysis in five years. 
Thanks for your help.

netstat:/etc/smokeping# diff /usr/share/perl5/smokeping/Smokeping.pm 
~mitchell/Smokeping.pm-patched
601c601
<         ("dummy", '--start', -$start,
---
 >         ("dummy", '--start', -$start,'--end','-'.int($start / 
$cfg->{Presentation}{detail}{width}),
807a808
 >            '--end','-'.int($start / $cfg->{Presentation}{detail}{width}),


> 
> cheers
> tobi
> 


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| David Mitchell (mitchell at ucar.edu)       Network Engineer IV  |
| Tel: (303) 497-1845                      National Center for  |
| FAX: (303) 497-1818                      Atmospheric Research |
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