[rrd-users] Question regarding missing data points

[Alex van den Bogaerdt]

Let me elaborate on this:

> rrdtool update test.rrd 1477433700:15
> # rrdtool update test.rrd 1477434000:NaN   # here is a missed measuring
> point
> rrdtool update test.rrd 1477434300:8

> Can anyone advise how to setup the rrd, so that one missing PDP gets
> exactly one NaN ?

The problem is that you get 2, not 1, unknown PDPs. That is because the
update at timestamp 1477434300 will fill all the time between the last
update (1477433700) and itself. The rate is unknown because of your
heartbeat settings.

As far as I know you cannot do something in RRDtool to say that updates
are for 300 seconds only and if there is more time not updated, it should
be processed as if it was updated with U. But who knows, maybe I'm missing
something.

Unless someone else comes up with a better solution, you will have to
update using U (for unknown) or accept that one more PDP will also be
unknown.  If the monitoring is offline for e.g. 55 minutes, the next
update will try to fill 12 PDPs which will all be unknown.

A quick hack, if you can spare the resources, is to update 300 seconds ago
with rate U and just ignore the error RRDtool will give you if that update
was already successfully done.

A less quick hack is to modify your scripts so that it remembers the last
update time (or queries it from the RRD) and looks at the difference with
now. If that is more than 300 seconds, then update with rate U and time
now-300s.