[rrd-users] Newby questions

[Tobias Oetiker]

Today Pablo Chacin wrote:

>
> Hi Tobi
>
> > 3. Finally, is there any patch to add SUM function for totalizing a
> > metric over a period. This is a very important requirement as we need to
> > count the total number of certain events for minute, hour and day. I'm
> > aware of the approach of using the average and multiplying by the
> > reporting period, but this will lead to a approximated value.
> >    everything in rrdtool is a 'rate' so even if there was such a
> >    function the math would still be the same ... can yo elaborate in
> >    what way you expect the result of the calculation to be an
> >    aproximation?
> >
>
> According to what I read in the previous discussions on this list
> (https://lists.oetiker.ch/pipermail/rrd-developers/2005-April/001405.html)
> The presence of  unknown values may produce wrong totals when
> calculating the total from the average. For example:
>
> >    0:UNKN 300:10 600:10 900:10
> >
> > consolidated and then mulitplied by the period will produce the same value
> > as if all entries were 10, and not with one UNKN (given the cf is 0.5). A
> > SUM function would nicely return 30.
> >

you can track the amount of unknown time too ... but you can use
the TOTAL function will ignore unknonwn values ...

otoh, why would you want to count UNKNOWN as ZERO ? isn't more
corect to asume that the values during the time where you have no
information were the same as in over the rest of the interval ?

cheers
tobi


> Regards
>
> Pablo
>
>
>
> On 10/29/2012 10:16 PM, Tobias Oetiker wrote:
> > Today Pablo Chacin wrote:
> >
> > > Greetings all
> > >
> > > I'm new to rrdtools. I'm actually still evaluating it as as tool for
> > > storing monitoring metrics.
> > > After reading the documentation and several discussions in this list and
> > > also in other forums
> > > I'm still confused about a couple of things.
> > > 1. How are subsecond timestamt reported? In several places it is
> > > mentioned the existence of these timestamps, but can't find any example
> > > of how to specify it in the update command, except when using "N" as
> > > timestamp.
> >    rrdtool update 1351545246.3897:394.33
> >
> > > 2. Supposing subsecond timestamps are supported by rrdtools, are they
> > > also supported by rrdcached?
> >    I think the version on github does support it ... the released
> >    version not.
> > > 3. Finally, is there any patch to add SUM function for totalizing a
> > > metric over a period. This is a very important requirement as we need to
> > > count the total number of certain events for minute, hour and day. I'm
> > > aware of the approach of using the average and multiplying by the
> > > reporting period, but this will lead to a approximated value.
> >    everything in rrdtool is a 'rate' so even if there was such a
> >    function the math would still be the same ... can yo elaborate in
> >    what way you expect the result of the calculation to be an
> >    aproximation?
> >
> > > Even when
> > > I understand the concerns about it not working properly in all
> > > situations, I think is a very common requirement. Simply can't believe
> > > nobody has done this ever, unless I'm completely wrong about the need of
> > > such function.
> > cheers
> > tobi
> >
> > > many thanks in advance
> > >
> > >
> > >
>
>
>

-- 
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