@@ -98,7 +110,7 @@ inserting its value just as if you had put a number at that place. The variable can also be used in the various graph and print elements.
Example: VDEF:avg=mydata,AVERAGE
Note that currently only agregation functions work in VDEF rpn expressions. +
Note that currently only aggregation functions work in VDEF rpn expressions. Patches to change this are welcome.
@@ -114,6 +126,31 @@ the script, just as if it were generated by a DEF instruction.<
At some point in processing, RRDtool has gathered an array of rates +ready to display.
+CDEF works on such an array. For example, CDEF:new=ds0,8,* +would multiply each of the array members by eight (probably +transforming bytes into bits). The result is an array containing the +new values.
+VDEF also works on such an array but in a different way. For +example, VDEF:max=ds0,MAXIMUM would scan each of the array members +and store the maximum value.
++
+Use CDEF to transform your data prior to graphing. In the above +example, we'd use a CDEF to transform bytes to bits before +graphing the bits.
+You use a VDEF if you want max(1,5,3,2,4) 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.
++
+the rrdgraph manpage gives an overview of how rrdtool graph works. the rrdgraph_data manpage describes DEF,CDEF and VDEF in detail. @@ -125,7 +162,8 @@ the script, just as if it were generated by a DEF instruction.<
Program by Tobias Oetiker <tobi@oetiker.ch>
-This manual page by Alex van den Bogaerdt <alex@ergens.op.het.net>
+This manual page by Alex van den Bogaerdt <alex@vandenbogaerdt.nl> +with corrections and/or additions by several people