[rrd-developers] stacking and the *UNKNOWN*

[Tobias Oetiker]

*> Alex writes:
*>
*> > *> first, second, and third data sets (stacked area), the third data set only gets
*> > *> plotted when the second data set is non-zero.
*> > 
*> > could it be that the pink data is *UNKNOWN* and not zero ? you can use a
*> > CDEF with IF and UN to turn UNKNOWN data into 0 ... 
*> > 
*> 
*> Tobi,
*> 
*> IMHO this behaviour is unexpected and not correct.
*> 
*> Either one of the next two may happen:
*> 
*> - Unknown data is height zero when stacked
*>  or
*> - Unknown data makes the whole series go unknown.
*> 
*> Reasoning:
*> 
*> - unknown data is not plotted -> #3 gets stacked on #1
*>  or
*> - The total is #1+#2+#3 --> #1+unknown+#3 == unknown.
*> 
*> My preference would be the first option, if I would like to know the
*> total (as opposite to all values separated) I would add them up and
*> get option two automatically.
*> 
*> Both ways have pros and cons, perhaps a discussion on developers is
*> the right thing to do. I leave it up to you to forward this message
*> (right now not cc'ed)

OK lets see what others have to say ... 

what happens at themoment is that the code draws each layer of the stack
sequentially and as soon as it stacks data onto top of unknown data the data
can not be visualized anymore ... 

    known 1   -> paints OK
    UNknown 2 -> contains *UNKNOWN* (will not paint)
    known 3   -> will not paint either because it should paint starting
                 from the *UNKNOWN* value not painted in 2

opinions ... ?

cheers
tobi

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