[rrd-users] rrd at the ragged edge (updates every second)

[Tobias Oetiker]

Rick,

Yesterday Rick Jones wrote:

> I've come to rrd via ntop (http://www.ntop.org/) which I'm looking at in
> the context of sFlow (http://www.sflow.org/) and receiving sFlow counter
> samples as often as once per second per interface.  RRD and its use by
> ntop seems rather ideal in that it has the concept of keeping so many
> samples at fine resolution, so many at a coarser and so on.  I've (or at
> least I think I have) cranked ntop's storage of values into RRD down to
> once per second, but the appearance of messages such as:
>
>
> > Mon Apr 18 15:06:07 2011  **WARNING** RRD:
> > rrd_update(/usr/local/var/ntop/rrd/interfaces/sFlow-device.2/sFlow/48/ifOutMulticastPkts.rrd)
> > error:
> > /usr/local/var/ntop/rrd/interfaces/sFlow-device.2/sFlow/48/ifOutMulticastPkts.rrd:
> > illegal attempt to update using time 1303164367 when last update time
> > is 1303164367 (minimum one second step)
>
> (Which may have appeared even before the rate was cranked down to every
> second, I must confess I'm not quite sure one way or the other) has me
> concerned about operations at the limit - in other words, ostensibly I
> have values going into the rrd once per second, but suppose that
> flutters back and forth across the second boundary?  Is it likely that
> is what happened above? That the update happened to hit just before the
> second rolled-over?
>
> In this instance I happen to be running 4.0.3 of ntop compiled from source, and:
>
> raj at tardy:~$ dpkg -l | grep rrd
> ii  librrd-dev 1.4.3-1ubuntu1 time-series data storage and display system (development)
> ii  librrd4    1.4.3-1ubuntu1 time-series data storage and display system (runtime library)
> ii  rrdtool    1.4.3-1ubuntu1 time-series data storage and display system (programs)

you can input time with millisecond precision, then this will not
happen

1303164367.002
1303164367.393

cheers
tobi

>
> for the RRD bits.
>
> thanks,
>
> rick jones
>
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>

-- 
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900