NaN values being saved in Whisper datafiles

[xneo64]

hi @lomik , With reference to https://bugs.launchpad.net/graphite/+bug/867882

Somehow I'm finding my whisper files to contain nan, and while this is valid from a python JSON spec, it's breaking the Grafana javascript code which parses the JSON from graphite. And causes an error and does not plot graphs.

Apparently carbon-cache was patched to eliminate such cases of writing nan to the whisper files. Can you look into this?

[xneo64]

to further illustrate, here's an example of the cpu data gathered from collectd. This data is replicated and pushed to two hosts, one runs go-carbon, and the other carbon-cache:

with go-carbon gives the below two occurrences:
whisper-dump.py /home/graphite/storage/dc1/apphost00/cpu/0/cpu/interrupt.wsp | grep nan
0: 1446541000, nan
0: 1446540960, nan

while with carbon-cache no nan is found in .wsp files. Looking up these timestamps in carbon-cache's wsp files, they're not to be found. It seems that the default behaviour here is to drop any write to whisper containing 'nan'

[xneo64]

hello again @lomik i was able to achieve this by adding the below condition in whisper.go before the write happens:

if !math.IsNaN(r.Value) {
    points[i] = &whisper.TimeSeriesPoint{Time: int(r.Timestamp), Value: r.Value}
}

naturally, in the beginning I also had to define importing of math

[ahayworth]

We are experiencing the same bug in production. Pull #27 fixes it (with tests, too!).

❤️