[rrd-users] Re: Problems with large counters?

[Darren Gamble]

Good day,

Sorry for my late reply.  I did not check my messages over the weekend.

> > I grabbed two sample counters- going from 1.1382094242105E+14 to
> > 1.1382517014663E+14 , for example.
> >

 
> could it be that you are not feeding rrdtool integers but numbers
> which got converted to float in the meantime and then back ?

No, the numbers I pasted there are exactly how they were fed into rrdtool.
Here's the actual command line.

/usr/bin/rrdtool update
/var/lib/rrdtool/px6wh.vc.shawcable.net-traffic_all_netapp.rrd
N:31048116096083:1.1382094242105E+14

.. and then...

/usr/bin/rrdtool update
/var/lib/rrdtool/px6wh.vc.shawcable.net-traffic_all_netapp.rrd
N:31049709264514:1.1382517014663E+14

The change in the first counter (the slightly smaller one) is recorded fine.
The change in the second one is recorded as zero.  I difference between the
two numbers is certainly significant enough that a program should be easily
capable of finding the difference.

The command is generated dynamically with PHP using its default output
format, BTW.

 this
> will cause you to loose precision at the low end, so that at some
> point the difference between two high numbers is becomming zero ...
> rrdtool has arbitrary precision when building the difference of
> two numbers ... there could be bugs in rrdtool too, just guessing
> ...

Perhaps rrdtool itself is doing some sort of conversion that causes it to
lose precision?  Or perhaps it doesn't properly understand the exponent?

============================
Darren Gamble
Planner, Regional Services
Shaw Cablesystems GP
630 - 3rd Avenue SW
Calgary, Alberta, Canada
T2P 4L4
(403) 781-4948

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