From acbc4860ec6b85e62f0710aab495113151524825 Mon Sep 17 00:00:00 2001 From: oetiker Date: Wed, 29 Apr 2009 06:52:25 +0000 Subject: [PATCH] added some remarks on CDEF versus VDEF to the docs -- Pablo Sanchez git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk/program@1797 a5681a0c-68f1-0310-ab6d-d61299d08faa --- CONTRIBUTORS | 1 + doc/rrdgraph_data.pod | 28 ++++++++++++++++++++++++++++ 2 files changed, 29 insertions(+) diff --git a/CONTRIBUTORS b/CONTRIBUTORS index 9fcddbd..2b0ba92 100644 --- a/CONTRIBUTORS +++ b/CONTRIBUTORS @@ -44,6 +44,7 @@ Mike Mitchell Mike Slifcak many rrdtool-1.1.x fixes Oleg Cherevko Otmar Lendl (lots of bugfixes) +Pablo Sanchez (CDEF vs VDEF) Patrick Cherry Paul Joslin Peter Speck eps/svg/pdf file format code in rrdtool-1.x diff --git a/doc/rrdgraph_data.pod b/doc/rrdgraph_data.pod index 95b1ec7..02f9663 100644 --- a/doc/rrdgraph_data.pod +++ b/doc/rrdgraph_data.pod @@ -90,6 +90,34 @@ the script, just as if it were generated by a B instruction. Example: C +=head1 About CDEF versus VDEF + +At some point in processing, B has gathered an array of rates +ready to display. + +B works on such an array. For example, I +would multiply each of the array members by eight (probably +transforming bytes into bits). The result is an array containing the +new values. + +B also works on such an array but in a different way. For +example, I would scan each of the array members +and store the maximum value. + +=head2 When do you use B versus B? + +Use B to transform your data prior to graphing. In the above +example, we'd use a B to transform bytes to bits before +graphing the bits. + +You use a B if you want I to return five which +would be displayed in the graph's legend (to answer, what was the +maximum value during the graph period). + +If you want to apply 'complex' operations to the result of a VDEF you have +to use a CDEF again since VDEFs only look like RPN expressions, they aren't +realy. + =head1 SEE ALSO L gives an overview of how B works. -- 2.11.0