rrdgraph_data - preparing data for graphing in rrdtool graph
DEF:<vname>=<rrdfile>:<ds-name>:<CF>[:step=<step>][:start=<time>][:end=<time>][:reduce=<CF>]
VDEF:vname=RPN expression
CDEF:vname=RPN expression
These three instructions extract data values out of the RRD files, optionally altering them (think, for example, of a bytes to bits conversion). If so desired, you can also define variables containing useful information such as maximum, minimum etcetera. Two of the instructions use a language called RPN which is described in its own manual page.
Variable names (vname) must be made up strings of the following characters
A-Z, a-z, 0-9, -,_ and a maximum length of 255 characters.
When picking variable names, make sure you do not choose a name that is already taken by an RPN operator. A save bet it to use lowercase or mixedcase names for variables since operators will always be in uppercase.
DEF:<vname>=<rrdfile>:<ds-name>:<CF>[:step=<step>][:start=<time>][:end=<time>][:reduce=<CF>]
This command fetches data from an RRD file. The virtual name vname can then be used throughout the rest of the script. By default, an RRA which contains the correct consolidated data at an appropriate resolution will be chosen. The resolution can be overridden with the --step option. The resolution can again be overridden by specifying the step size. The time span of this data is the same as for the graph by default, you can override this by specifying start and end. Remember to escape colons in the time specification!
If the resolution of the data is higher than the resolution of the
graph, the data will be further consolidated. This may result in
a graph that spans slightly more time than requested.
Ideally each point in the graph should correspond with one CDP
from an RRA. For instance, if your RRD has an RRA with
a resolution of 1800 seconds per CDP, you should create an
image with width 400 and time span 400*1800 seconds (use appropriate
start and end times, such as --start end-8days8hours).
If consolidation needs to be done, the CF of the RRA specified in the
DEF itself will be used to reduce the data density. This behaviour can
be changed using :reduce=<CF>. This optional parameter
specifies the CF to use during the data reduction phase.
Example:
DEF:ds0=router.rrd:ds0:AVERAGE
DEF:ds0weekly=router.rrd:ds0:AVERAGE:step=7200
DEF:ds0weekly=router.rrd:ds0:AVERAGE:start=end-1h
DEF:ds0weekly=router.rrd:ds0:AVERAGE:start=11\:00:end=start+1h
VDEF:vname=RPN expression
This command returns a value and/or a time according to the RPN statements used. The resulting vname will, depending on the functions used, have a value and a time component. When you use this vname in another RPN expression, you are effectively 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. Patches to change this are welcome.
CDEF:vname=RPN expression
This command creates a new set of data points (in memory only, not in the RRD file) out of one or more other data series. The RPN instructions are used to evaluate a mathematical function on each data point. The resulting vname can then be used further on in the script, just as if it were generated by a DEF instruction.
Example: CDEF:mydatabits=mydata,8,*
the rrdgraph manpage gives an overview of how rrdtool graph works. the rrdgraph_data manpage describes DEF,CDEF and VDEF in detail. the rrdgraph_rpn manpage describes the RPN language used in the ?DEF statements. the rrdgraph_graph manpage page describes all of the graph and print functions.
Make sure to read the rrdgraph_examples manpage for tips&tricks.
Program by Tobias Oetiker <tobi@oetiker.ch>
This manual page by Alex van den Bogaerdt <alex@ergens.op.het.net>