[rrd-users] Re: Getting the timestamp corresponding to MAX value

Kevin Elliott kelliott at dhapdigital.com
Fri May 12 19:39:25 MEST 2006

Tobias Oetiker wrote:
> Hi Kevin,
> since rrdtool is working at a predefined step size there is an
> inherent problem in recording particular events. The way to go
> about this is to store them when they occur alongside your RRD
> database in a format where you can store time:event ... then you
> can integrate these things into the RRD graph while producing it by
> supplying appropriate VRULE commands ...
> hope this helps
> tobi

Thanks for your response, I think this will help, although I need some 
clarification, and perhaps you can provide some advice on how to handle 
another situation (somewhat related) as well.

First, storing the events alongside is not a problem, although I'm not 
exactly sure how to incorporate that data using VRULEs when using drraw, 
cricket, or cacti. Furthermore, while storing this data flatly doesn't 
inherit much development overhead, tracking peak range values then 
becomes a task, almost duplicating some of the functionality of the rrdb 
already. For example, we'll have to write code to handle rules of value 
ranges and conditions. Clearly not an issue for a few things to monitor, 
but when you monitor hundreds or thousands of services, this could get 
fairly intense.

Second, the smoothing issue is fairly confusing for us, because we have 
many scenarios where we don't need or want smoothing, but would just 
prefer that particular value to fill the corresponding timeslot. For 
example, if I am monitoring an object that can only have 4 values, 0, 1, 
2, and 3, I never want to see 0.2 or 1.6. A square graph would be more 
than sufficient. Further, so let's say our step was supposed to be at 
time X but we actually updated it at X+32secs, store whatever the value 
was for X, rather than try to determine what it COULD have been at that 
time. We are all a little confused why this functionality couldnt 
coexist! For example:

STEP 1   2
STEP 2   2
STEP 3   2
STEP 4   4
STEP 5   1
STEP 6   2

So, when graphed, we'd like to see it spike up to 2, then hover across 
for three time points, then immediately jump up to 4, go across one 
step, then down, etc.
-----|     |

What are your thoughts?


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