[rrd-users] Re: disabling interpolation?

[Rainer Bawidamann]

>> Wrong.  You can't say that at all.  You could very easily say that
>> the minimum amount of people in the room as 0 and the maxium amount
>> was 12, and I could still give you a scenario where the average as
>> 4.76

> Ack, this can happen.  Also, you never know for sure that it did or did
> not happen (with our way of monitoring).  At least I *can* be sure that
> the *actual* number of people (and *not the average*) was not 4.76  This
> is what the discussion is about:  is it proper to first average and then
> use max/min on it?

I think as long as you have only information about how many people are
currently logged is to hard to get the true maximum: you have to query
the information as often as it's possible to login (as often as the
value can change).

In fact you need the information "maximum of number or users
simultaneously logged in since x" where x could be the last time this
information was queried. Now a DST of REAL would be useful.

If you don't have this information (from a radius log e.g.) you should
use the "average maximum" numbers from rrdtool and explain the odd
values.

> I never got 4.76 and therefore I do not want to see 4.76 ...

If you measure an approximation of a value you cannot get the real
value from this.


Conclusion: rrdtool is limited to store data at fixed intervals (*). If
you cannot get your true maximum values at these fixed intervals you
cannot use rrdtool to store your data.

(*) you cannot store values at x+0, x+5, x+7, x+11 because rrdtool will
    alter them.


Rainer

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