[rrd-users] Math in VDEFs

[Tobias Oetiker]

Hi Marco,

The lack of math abilities in VDEF is a miss-feature, it is a
matter of time ... and focus ...

patches or sponsorship welcome

cheers
tobi


is Today Marco Chiappero wrote:

> Hi everybody,
> I have an unusual question for you.
> As you know it's not possible to do mathematical operations in VDEFs. Is
> it by design? Or math is simply lacking and will be implemented in the
> future? Ok, you can argue that CDEFs are there for such a purpose, but
> why should be bad to do calculus on just a single data point rather than
> a whole set? Let me show you an example, maybe too much didactic but
> still meaningful, that made me think about this.
> Let's say you want to plot uptime informations from a server of yours,
> in the legend you can show the current uptime and for example the
> longest run (maybe the shortest one too) and the average uptime during
> the last year. It looks pretty easy, you have just to move the entire
> data set from seconds to days dividing by 86400 seconds/day and then
> choose the average, maximum, etc. Now let's suppose you want to print
> information using the 'uptime' command output schema, thus days, hours,
> seconds separately. You can't do that anymore, because you have to do
> math calculation after choosing the average or maximum. Well, it's still
> quite simple form the logic point of view, select the value you want
> from the DEF, in seconds, and then apply three different VDEF
> calculation on that one, but currently you can't.
> However I managed to get the same output another way (adding a
> particular CDEF) but with more complexity, in my opinion too much for
> such a simple purpose.
> So I'm asking: is there a reason for not to have math operators in
> VDEFs? Is it by design or it's just a matter of time?
> Thank you.
>
> Regards,
> Marco Chiappero
>
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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