[rrd-developers] Bug#543631: rrdupdate does not support floating point values with DERIVE, COUNTER

[Tobias Oetiker]

Dec 28 Sebastian Harl wrote:

> Hi,
>
> (This is a follow-up to Debian [bug543631].)
>
> On Wed, Aug 26, 2009 at 08:00:22AM +0000, Florian Weimer wrote:
> > Floating point values are supported with GAUGE.  This suprising
> > behavior is not clearly documented, as far as I can tell.  I don't
> > think there are architectural reasons for this behavior.
>
> [side note: "this surprising behavior" refers to the subject of the
> E-mail, i.e. "rrdupdate does not support floating point values with
> DERIVE, COUNTER" ;-)]
>
> I'm not entirely sure about any reasons for that either. COUNTER and
> DERIVE values are stored as a rate (i.e., a double) as well anyway. To
> be able to calculate the rate, the last value is stored as well. This is
> done using a string, though, so it does not impose any limitations
> either.
>
> With this E-mail, I'm forwarding the issue upstream, hoping for an
> explanation (or request for patches ;-)).

the reason for this is that rrdtool does the integer math for
building the difference between two counter values 'by hand' with
the advantage of being able to handle really long counters ...

OTOH with long long being available across the board, this might be
a bit of a anachronism ... not quite sure though, what happens when
you diff two doubles realy close to 2^64 ... does this stay
accurate enough ? I guess a little magic would still be needed
there ... care to investigate ?

cheers
tobi

>
> Cheers,
> Sebastian
>
> [bug543631] http://bugs.debian.org/543631
>
>

-- 
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