[rrd-users] trying to understand the relationship between source data, what's in rrd and what gets plotted

Mark Seger Mark.Seger at hp.com
Sat Jul 21 15:42:47 CEST 2007

> Please let me summarize in my own words:
> If you display 4000 rates on a 400-pixel wide graph, you want to
> see 10 dots per column, not a line or an area connecting an
> minimum, average, maximum or last.
> Correct?
correct, but a line can be useful too!
> If so:
> This would require programming (in rrd_graph.c and friends).
> In my example of 10 dots per column, how do you suggest RRDtool graph
> should show these rates: 1 1 1 3 4 7 7 7 7  ?
> Should it show 6 dots of equal size,
> should it show 2 large dots and two small dots,
> or ... ?
Just put the dots (or lines) where they belong and if some fall on top 
of each other and you only see 6, that's just fine.  Where I'm coming 
from, and what I always do with performance related data, is look at a 
broad range of time, perhaps a day wide.  I want to look at everything 
from cpu load, network, disk, memory usage, infiniband loading and a 
whole lot more.  I want to be able to see at a glance if there are any 
spikes where there shouldn't be or drops that also shouldn't be there.  
If nothing shows up, I'm done and that's why it's so critical that 
everything be displayed.  If there is a problem THEN I want to zoom in 
and the resolution becomes more significant and those dots/lines then 
begin to spread out as the resolution increases.  Quite frankly I don't 
look at consolidated data because it's those exceptions that are the 
most significant when trouble shooting.
> If my summary is not correct, then what do you mean?
perfect, but as I also said I wouldn't want to just be limited to dots 
as sometimes they are hard to see and that's where connected lines can 
be more useful.  quite honestly I use both but do tend to focus on 
lines.  you see I'm color blind and a little dot falling at the top or 
bottom of a graph can be easily missed whereas a spike is much more obvious.


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