[mrtg] Re: MRTG not saving history of plot in .log files

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Sat Oct 6 14:03:08 MEST 2001

Oliver Schulze L. wrote:

> I get some 200 emails per day, so I think that I don't get more than 0
> emails per seconds.
> Should I use a perminute option for this setup?

That's probably not good enough.  Unless you receive your mail
by five at a time, you still end up with numbers below 1 (assuming
the default sample period of 300 seconds).

  sample at time "T" shows there are 10 emails received
  sleep 300
  sample at time "T+300" shows there are 11 emails received

Delta_emails is 1, delta_time is 5 (minutes, we're using per minute)

Calculation of "rate":  delta_email / delta_time == 0.2
MRTG works with integers so this 0.2 is truncated to 0.

If you'd try and sample only once per day:

at time "T" the number is 0
at time "T+86400" the number is 200
Difference is 200 and 86400, rate is:
normal:    200/86400  == 0.0023148148  --> 0
perminute: 200/1440   == 0.1388888888  --> 0
perhour:   200/24     == 8.3333333333  --> 8

If you calculate the number of emails from the rate:
0*86400 = 0 emails
0*1440 = 0 emails
8*24 = 192 emails (and not the 200 you've really transfered)

As you can see MRTG is not very good in these low numbers.  You could
have a peek at RRDtool and see if that works for you.  However, you
will get results like "2.3148148 milimail per second" which is a proper
presentatin however some people think it is not done to talk about

 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
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