--- /dev/null
+=head1 NAME
+
+rrdgraph_data - preparing data for graphing in rrdtool graph
+
+=head1 SYNOPSIS
+
+B<DEF:>I<E<lt>vnameE<gt>>=I<E<lt>rrdfileE<gt>>:I<E<lt>ds-nameE<gt>>:I<E<lt>CFE<gt>>[:step=I<E<lt>stepE<gt>>][:start=I<E<lt>timeE<gt>>][:end=I<E<lt>timeE<gt>>][:reduce=I<E<lt>B<CF>E<gt>>]
+
+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, minimum etcetera. Two of the instructions use
+a language called B<RPN> which is described in its own manual page.
+
+=head1 DEF
+
+B<DEF:>I<E<lt>vnameE<gt>>=I<E<lt>rrdfileE<gt>>:I<E<lt>ds-nameE<gt>>:I<E<lt>CFE<gt>>[:step=I<E<lt>stepE<gt>>][:start=I<E<lt>timeE<gt>>][:end=I<E<lt>timeE<gt>>][:reduce=I<E<lt>B<CF>E<gt>>]
+
+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 overridden with the L<--step|rrdgraph/item_Time> option.
+The resolution can again be overridden by specifying the B<step size>.
+The time span of this data is the same as for the graph by default,
+you can override this by specifying B<start and end>. Remember to
+escape colons in the time specification!
+
+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>).
+
+If consolidation needs to be done, the B<CF> of the B<RRA> specified in the
+B<DEF> itself will be used to reduce the data density. This behaviour can
+be changed using C<:reduce=I<E<lt>B<CF>E<gt>>>. This optional parameter
+specifies the B<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
+
+=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.
+
+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,*>
+
+=head1 SEE ALSO
+
+L<rrdgraph> gives an overview of how B<rrdtool graph> works.
+L<rrdgraph_data> describes B<DEF>,B<CDEF> and B<VDEF> in detail,
+L<rrdgraph_rpn> describes the B<RPN> language used in the B<?DEF> statements,
+L<rrdgraph_graph> page describes all of the graph and print functions.
+
+Make sure to read L<rrdgraph_examples> for tipsE<amp>tricks.
+
+=head1 AUTHOR
+
+Program by Tobias Oetiker E<lt>oetiker@ee.ethz.chE<gt>
+
+This manual page by Alex van den Bogaerdt E<lt>alex@ergens.op.het.netE<gt>
projects / rrdtool.git / blobdiff