[rrd-users] Additional "Unknown"-Value

n1LL3 Christian.Michel at it-novum.com
Wed Jun 10 12:17:59 CEST 2009

oetiker wrote:
> My sugestion would be that you set your mrhb to only a bit more
> than your sampleing interval ... (as it should be) now, when you
> miss samples, or you log 'U' rrdtool will turn the stored data into
> NaN aka Unknown which will cause the graph to 'disapear' ...
> My phanstasy is that you want to see the graph break for intervals
> shorter than your step size ?
> cheers
> tobi

Hello Tobi,

good idea! At first we want to solve our problem like this as well, but then
other problems will occure. 

For various reasons it could be that the RRD can not be updated in
continuous time intervals, for e.g.:
- system-latency
- network-latency
- reload of the monitoring tool 
- restart of the server

For that time we have no data for the RRD, but we want to handle it like "in
dubio pro reo" ("in doubt for the accused"). In this case it would be nice
if we could have the ability to set the mrbh such high that only very long
timeperiods (longer than one day) will not be bridged. 
But if there will be a real problem while monitoring something (performance
data could not be determined for example due to timeout), it would be good
to have the option to tell RRDtools that it was determined an
This breakdown will be displayed in the graph as well without overwriting
the breaks by aggregation or additional filling of the graph by using a
small heartbeat.

Otherwise it could be fatal, because we want to create service level
Without this function the SLAs will have wrong results.
Maybe this could also be very interesting for other monitoring tools.

I hope you can comprehend what I mean.


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