[rrd-users] First gauge value isn't stored - what am I doing wrong?

Joachim Schrod jschrod at acm.org
Tue Dec 1 02:12:32 CET 2009

A Darren Dunham wrote:
> On Mon, Nov 30, 2009 at 06:08:20PM +0100, Joachim Schrod wrote:
>>     rrdtool create test.rrd --start '00:00 24.11.2009' \
>>         --step 86400 DS:count:GAUGE:172800:0:U RRA:MAX:0.9:1:30
>> Now I simulate the 1st measurement:
>>     rrdtool updatev test.rrd '00:30 24.11.2009'@1573
>> Now, 2nd measurement the next day:
>>     puma:data $ rrdtool updatev test.rrd '00:30 25.11.2009'@1574
>>     return_value = 0
>>     [1259020800]RRA[MAX][1]DS[count] = NaN
>> Oops? Why is NaN stored here for the Nov 24 value?
> Hmm.  I can't replicate this.
> What version of RRD are you using, and what is your TZ variable set to?  

Thanks, thanks! localtime was the culprit.

I'm at CET, i.e., test.rrd hat actually a start time of 23:00 UTC
and not of 00:00 UTC. Thus, the jobs ran at 23:30 UTC, not at
00:30. If I adapt start time and measurement time to proper UTC
entries, it works. I.e., I'll have to start my cron job not earlier
than 03:00 local clock (to care for DST switches) and it should work.

This information will enable me to continue in my rrdtool exploration.

Though I have to confess that I still don't really understand why
the first entry was not stored. After all, it was the only primary
data point for the interval 2009-11-23 23:00 UTC to 2009-11-24
23:00 UTC; and from the documentation I would have assumed the only
PDP in the interval START+STEP not to get lost.

Btw, version number seems to be irrelevant for that behaviour. I
tried it with 1.4.1 on CentOS 5.2 and still got the same results.

Thanks again for your pointer that enables me to continue,


Joachim Schrod				Email: jschrod at acm.org
Roedermark, Germany

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