[rrd-users] Inserted value becomes NaN

Simon Hobson linux at thehobsons.co.uk
Thu Jan 15 18:12:45 CET 2015

Jon August <jonaugust at gmail.com> wrote:

> I do an update like this:
> rrdtool updatev filename.rrd N:1102
> What am I doing wrong?

One update does not create a value in the database - it merely sets a "known point", and for the very first update, all data up to that point is unknown. You need to make repeated updates over a period of time. Once you pass the *END* of a data point, then a value will be computed for the previous interval - but only if enough data has been entered for the interval to have a valid value, that's what the "fudge factor" (0.5 in your example) is for.

So in your case, you need multiple updates, not more than 48 hours apart (or the data becomes unknown again), and after the end of a day* you will get a value if you have enough data to fill the previous 12 hours (0.5 x 1day) with valid data.

* Note that a day will start/end at midnight UTC. All intervals end at an integer multiple of "step" after midnight Jan 1 1970 (unix epoch).

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