rrd gaps <Virus checked>

[Steffen Poulsen]

> > From my experience, gaps are normally caused by missing 
> datasets over 
> > a period of time. RRD expects data within a time window 
> defined in the 
> > "step" and "heartbeat" variables. If data doesn't arrive in this 
> > window, the value for the defined time frame is set to "NaN" (Not a 
> > number), resulting in not being displayed in the generated image.
> > 
> > Missing datasets are often caused by:
> > 
> > - Huge service latencies, e.g. if you got lots of services to be 
> > checked in a rather short period of time. (Got this with 3k 
> services, 
> > which should be checked in a period of 2 minutes -> 25 
> Checks/second 
> > is quite a lot...)
> > 
> > - non-fitting service check intervals. If you check your 
> services in a
> > 15 minute interval, but your rrd files expect data every 5 minutes, 
> > only every third time frame will be filled, resulting in gaps.
> > 
> > Maybe this is of some use.
> 
> It is, it explains a lot. I'll do some adjustments and tests 
> and report back to this thread.

If you report in only every 15 minutes, you will be plain lucky to have
any graph at all. You are required to have two entries inside the same
heartbeat to get a graph drawn (as far as we understand it). The default
heartbeat in the nagios grapher version we installed was 900 (15
minutes).

We recently chose to raise the heartbeat to one hour, so services
scheduled with more than 15 minutes between checks also have a chance of
creating a graph.

We used rrdtool and this little script to assist in the process of
updating our existing rrd files (use with find --exec)

#!/bin/sh
# Update heartbeat values for all datasources in rrd file
# Usage update_rrd_heartbeat.sh <file> <heartbeat>

rrdtool info $1 | grep ds | grep minimal_heartbeat |  perl -pe
's/^ds.*?\[(.*?)\].*?$/$1/g' |
        while read line
        do
          if [ -n "$line" ]; then
            echo "updating $line ds in $1"
            rrdtool tune $1 -h $line:$2
          fi
        done 

Best regards,
Steffen Poulsen

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