[rrd-developers] Ask for new CDEF TREND function in next RRDTool release

[Didier]

Ask for new CDEF TREND function in next RRDTool release


Hello dear Developers of the RRDTool,

   Thanks a lot for your RRD tool.
   It's very nice. I'm using it with Cacti frontend.
   I'd like to have a new feature in RRD Tool that's why I'm writing you.
   I hope you could integrate it in the next release of RRD Tool.

Let me explain

   I'd like to have a new CDEF function in the graphs.
   I'll call this fucntion for instance  TREND  or  PASTAVG (as past average)

   It would work like that

     DEF variable=rrd:ds-name   ---------> nothing change here it is just to undestand what is 'variable'
     CDEF vname=variable,delay,TREND

   For instance
     DEF a=rrd:ds-name 
     CDEF vname=a,1800,TREND       ---> To have a trend for last 1800s=30 minutes

   The purpose of this TREND CDEF would be to compute trends over the 'delay' specified (delay in seconds).
   More precisely it would be the average of the 'variable' during the last 'delay' time starting form the sample
   'delay' will be expressed in seconds


   Below I have represented an RRD

            !---!---!---!---!---!---!---!---!---!
                                               now

                       delay    t
                 <-------------->
                 
                         delay     t+1
                     <-------------->  
  
                              delay     t+2
                         <-------------->


     The trend value at sample (t) will be the average between  (t-delay)  and  (t)
     The trend value at sample (t+1) will be the average between (t+1-delay) and  (t+1)
     The trend value at sample (t+2) will be the average between (t+2-delay) and  (t+2)
     And so on, do you understand ?


     So the trend is not a fix value as HRULE could be
     When delay is a very short time ---> It will allow to represent a short time trend
     When delay is a very long time  ---> It will allow to represent a long time trend            
                    



   I think this function would be very usefull to add on one graph a curve, a hort trend for this curve computed with delay of 30 minutes) for instance,  a middle trend (computed with delay of 1 month), and long trend (computed with delay of 1 year).
   In this way we could compare more easily the curves to what they should be, that is to say to their baseline.
   I think many people will be interested in.  



   As a workaround, may be there is a way to do that with the TIME CDEF but I haven't found, it is very complex with it.
   With this new  TREND  CDEF it will be easier to do that.


   I hope you will find this proposition all right for a next release of RRD tool.
   I would appreciate if you can answer me on that point

  Thanks

Didier
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