[rrd-users] Re: Question

[Fruitman, Corey]

Hi, Christoph.

You need to create a CDEF to get the timestamp of the current measurement first.  Since RRDTool requires that you have to have a variable in your CDEF, take any variable, subtract it from itself (which produces zero) and then add the TIME.  Your next CDEF can get the PREV of that (ie, the previous timestamp), and RRDTool is happy.

A bit confusing, I know.  Here's an example...

CDEF:mytime=TIME,idefix2_content,idefix2_content,-,+ CDEF:prevtime=PREV(mytime)

Now prevtime holds the timestamp of the previous measurement.  You can use the PREV function again in another CDEF to get the measurements that correspond to prevtime.

Hope that helps.

Corey.

-----Original Message-----
From: Christoph Galuschka [mailto:christoph.galuschka at tikom.at]
Sent: August 4, 2003 9:30 AM
To: rrd-users at list.ee.ethz.ch
Subject: [rrd-users] Question


Hi,

what I would like to know is: What is the correct function to 
produce a virtuall dataset with the same data as its 
predecessor, only one timestep behind (or ahead, doesn't 
matter).

Let's say, I have the following:
DEF:idefix2_content=/pathtorrd/idefix2_content.rrd:idefix2_con
tent:AVERAGE

as dataset, and I would like to create virtuall dataset from 
this. How does the CDEF-Line have to look like?

thanks in advance and regards
Christoph

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