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

Joachim Schrod jschrod at acm.org
Tue Dec 1 11:45:53 CET 2009

Simon Hobson wrote:
> 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
> Note that all sample periods start at n*S from unix epoch (where
> s is sample period)

Thanks - that's the sentence that I would have needed in the
documentation to make me understand the behaviour. This is neither
noted in rrdcreate man page nor in any of the tutorials that I read.

For my actual task, taking measurements in UTC is OK, I need
measurement-in-day accuracy, but should not loose data points. So
I'll step up my heartbeat massively to avoid the problem of
interrupting my time series.

> - so specifying a full day (86400s) means sample periods will 
> ALWAYS start/finish at midnight UTC.
> You should read Alex's tutorial on normalisation.
> http://www.vandenbogaerdt.nl/rrdtool/

I've read it now, and quite honestly, I wouldn't have understood
its implications for my problem. It's not explained how the
normalization target intervals are defined (which was the crucial
missing information), only that they exist and that they are "well
defined". It is also not explained that if my source interval only
covers a small part of my target interval and the rest is unknown,
my measurement is dropped. (I thought so at some point and changed
my RRA xff ratio to 0.99999999, but that didn't change anything.)

So thanks again for taking time to explain the basics.


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

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