[rrd-users] Re: how to fill with previous value when graph

Dexin Wang dexin at rtda.com
Thu May 15 03:39:16 MEST 2003

Thank you very much, Dan. I didn't understand why your first suggestion 
would solve my problem. I also tried settign xff to 0.99, and I read the 
tutorial. So far still not getting the solution.

Let me state my questions again here:

Say my step is 1 second. On the 1st, 2nd, 3rd second, I store some 
value. But I don't have any values for 4th, 5th, 6th second and what I 
want is that 4th, 5th, 6th second's value == the value on the 3rd 
second(previous non-NaN value). How should I create the database, and 
how should I do graph?

I appreciate any of your help.



Dan McGinn-Combs wrote:
> Last time I tried to use a recursive value like that, it didn't work. I
> think you want the other "value" to be separate previously defined,
> right?
> DEF:count=counter.rrd:DS0:AVERAGE
> CDEF:value=count,UN,0,count,IF
> One other option is to set the XFILES very high so that you are
> virtually assured of having SOME reading. It is by convention set to .5
> so that if half the returned readings are NaN, they are stored as NaN.
> By setting it to .99, it will always store some reading, not matter how
> small.
> You might check the following URL to see some examples of the RPL
> language. I found the exceptionally hepful:
> http://www.rrdtool.com/tutorial/rpntutorial.html
> http://www.rrdtool.com/tutorial/cdeftutorial.html
> Dan
> -----Original Message-----
> From: Dexin Wang [mailto:dexin at rtda.com] 
> Sent: Wednesday, May 14, 2003 6:52 PM
> To: rrd-users at list.ee.ethz.ch
> Subject: [rrd-users] how to fill with previous value when graph
> I have some NaN value on some PDP. When creating the graph, I know I can
> do this:
> CDEF:value=value,UN,0,value,IF
> to set the value to 0 if it is NaN. Is it possible that whenever I find 
> a NaN, I use the value of the previous non-NaN PDP? Basically can I 
> store value in a variable and use it? Or some other way? Please help.

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