[rrd-users] Inserted value becomes NaN

[Jon August]

I created an RRD file with this:
rrdtool create filename.rrd \
--step '86400' \
--start '1388534400' \
'DS:devices:GAUGE:172800:U:U' \
'RRA:AVERAGE:0.5:1:365'
I want to store the number of devices on a network daily.

When I try to do an update, the RRA dump shows NaN. As if the value was ignored. I do an update like this:

rrdtool updatev filename.rrd N:1102

What am I doing wrong?

Thanks,
-Jon

[Simon Hobson]

Post by Jon August
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).

[Jon August]

Got it.

Thanks for the clarification.

-Jon

Post by Simon Hobson

Post by Jon August
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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