[mrtg] Re: MRTG Error doing uprate

[Rich Adamson]

Mrtg has had a problem for some time with handling zero values under
some circumstances. The problem originated sometime around v2.9.17 (or
earlier) and continued in various forms within the v2.9.18pre? releases. 
At least some of the pre? releases attempted to fix the problem, but 
created another instead. I'm not sure that problem is fixed in any current
release right now.

The original problem was identified when mrtg missed an snmp poll, it
was thought that missed poll inserted a zero value into the log file.
The next "valid" poll understood the previous poll was missed and
attempted to hide that fact by calculating a "fake" historic value
(apparently for averaging purposes). The fake value calculation is not
correct resulting in a hugh spike on the chart under some circumstances.

Depending upon exactly which "pre?" release you implement, you may see
differing zero-value results as someone attempts to correct the original 
problem.

------------------------
> First of all, maybe this wouldn't be the appropiate list to explain my
> problem and I apologize if someone thinks so.
> 
> I'm using MRTG to graph BGP4 Prefixes announced to my AS from my peering
> neighbours, I use an external script that grabs the info and give the data
> to MRTG in the following format:
> 
> print "$dataIn\n";
> print "$dataOut\n";
> print "$uptime\n";
> print "$description\n";
> 
> This is the correct format and I've been using it (and it worked fine) but
> when I updated to mrtg-2.9-18pre3 (I don't know exactly what was the older
> version I was using, maybe 2.9.13) when $dataOut is equal to 0 both
> variables appears as 0 in the graph... I've test everything... I've written
> a perl script like:
> print "0\n";
> print "100\n";
> print "0\n";
> print "0\n";
> 
> and get 0's in in and out but if I used:
> print "100\n";
> print "0\n";
> print "0\n";
> print "0\n";
> 
> the incoming variable is 100 and outgoing is 0... why? Someone can explain
> it? Or if it's just a bug, where should I report it?
> 
> Thanks in advance,
> David Manchado
> 
> 
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