complete rewrite of rrdgraph documentation. This also includs info

[rrdtool.git] / doc / rrdgraph_data.src

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+=include name
+
+=head1 SYNOPSYS
+
+B<DEF>:I<vname>=I<RRD file>:I<ds name>:I<CF>[:[I<time range>][:I<step size>]]
+
+B<VDEF>:I<vname>=I<RPN expression>
+
+B<CDEF>:I<vname>=I<RPN expression>
+
+=head1 DESCRIPTION
+
+These three instructions collect the data out of the B<RRD> files,
+optionally altering it (think of a bytes to bits conversion) and
+if desired you can define variables containing useful information
+such as maximum, mininimum etcetera. Two of the instructions use
+a language called B<RPN> which is described in its own manual page.
+
+=head1 DEF
+
+B<DEF>:I<vname>=I<RRD file>:I<ds name>:I<CF>[:[I<time range>][:I<step size>]]
+
+This command fetches data from an B<RRD> file.  The virtual name
+I<vname> can then be used throughout the rest of the script. By
+default, an B<RRA> which contains the correct consolidated data
+at an appropriate resolution will be chosen.  The resolution can
+be overriden with the L<--step|rrdgraph/item_Time> option. 
+I<Not yet implemented:>[ The resolution can be overriden by specifying
+the B<step size>.]  I<Not yet implemented:> [ The time span of this data
+is the same as for the graph by default, you can override this by
+specifying the B<time range>. ]
+
+If the resolution of the data is higher than the resolution of off
+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 B<CDP>
+from an B<RRA>.  For instance, if your B<RRD> has an B<RRA> with
+a resolution of 1800 seconds per B<CDP>, you should create an
+image with width 400 and time span 400*1800 seconds (use appropriate
+start and end times, such as C<--start end-8days8hours>).
+
+Example: C<DEF:mydata=router.rrd:ds0:AVERAGE>
+
+Example: C<DEF:januari=router.rrd:ds0:AVERAGE:start=20010101 end=20010201>
+
+=head1 VDEF
+
+B<VDEF>:I<vname>=I<RPN expression>
+
+This command returns a value and/or a time according to the B<RPN>
+statements used. The resulting I<vname> will, depending on the
+functions used, have a value and a time component.  When you use
+this I<vname> in another B<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. I<Not yet implemented:> [ Everywhere you can insert a
+number, you can also use the B<VDEF> (provided that it is set of course) ]
+
+Example: C<VDEF:avg=mydata,AVERAGE>
+
+=head1 CDEF
+
+B<CDEF>:I<vname>=I<RPN expression>
+
+This command creates a new set of data points (in memory only, not
+in the B<RRD> file) out of one or more other data series. The B<RPN>
+instructions are used to evaluate a mathematical function on each
+data point. The resulting I<vname> can then be used further on in
+the script, just as if it were generated by a B<DEF> instruction.
+
+Example: C<CDEF:mydatabits=mydata,8,*>
+
+=include see_also