[mrtg-developers] Re: How many Routers we can poll using MRTG

Tobias Oetiker oetiker at ee.ethz.ch
Fri Sep 29 10:54:14 MEST 2000

Today you sent me mail regarding Re: [mrtg-developers] Re: How many Routers...:

BN> Tobias Oetiker wrote:
BN> > Today you sent me mail regarding [mrtg-developers] Re: How many Routers we...:
BN> > BN> > 2. If the polling doesn't finish by 5 minutes, when cron tries to start
BN> > BN> > the second mrtg what happens.
BN> > BN> 
BN> > BN> The new job will die and the old one will finish. With rateup, this
BN> > BN> wasn't a big problem, but with rrdtool the graphs gets really ugly.
BN> > 
BN> > *  can you elaborate on the 'ugly' bit ?
BN> With rateup, an unknown value is represented by the last known value
BN> when the graph is drawn. rrdtool uses zero instead, and the graph may
BN> not be continuous as it will drop to zero for every unknown value.
BN> Also, this seems to be a problem when detecting errors in the statistics.
BN> An line with no traffic is quite usual, a line which has flatlined on,
BN> say, 6.4Mbps, will be notices immediately. This is just psychological;
BN> the more green the easier to spot an error. :-)

well in rrdtool you can do even better, by writing a CDEF which
looks out for UNKNOWN and produces a high value when the imput is
unknown and UNKNOWN when the value is normal ... you can then drwa
the result of the cdef as a LINE3: in red ... and unknown will
suddenly become VERY noticable ... 

check the rrdtool mailinglist archives this has been discussed at
length ... 


BN> > *  you may want to use the daemon mode then the mrtg will run
BN> >    continuously if it does not finish withing the interval
BN> Yes, I did consider that, however a few problems arose:
BN> - What *if* the daemon dies? (I would need to write a wrapper)
BN> - What if the config file changes? (It does every 3 hours)
BN> I think I had a few other points to when I chose not to run in
BN> damon mode, but I can't remember them now. Anyway, I will re-
BN> consider it some time when things cool down a little here.

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