diff --git a/doc/rrdgraph_data.pod b/doc/rrdgraph_data.pod
index 5b71c87f94b924c452fb3416a5cd5050cebcfaeb..fc0c2fc360669ed788e20042f7ad92ae9ace4c45 100644 (file)
--- a/doc/rrdgraph_data.pod
+++ b/doc/rrdgraph_data.pod
instructions use a language called B<RPN> which is described in its
own manual page.
+Variable names (I<vname>) must be made up strings of the following characters
+C<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 safe bet it to use lowercase or
+mixedcase names for variables since operators will always be in uppercase.
+
=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>>]
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.
+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
Example: C<VDEF:avg=mydata,AVERAGE>
+Note that currently only aggregation functions work in VDEF rpn expressions.
+Patches to change this are welcome.
+
=head1 CDEF
B<CDEF>:I<vname>=I<RPN expression>
=head1 AUTHOR
-Program by Tobias Oetiker E<lt>oetiker@ee.ethz.chE<gt>
+Program by Tobias Oetiker E<lt>tobi@oetiker.chE<gt>
This manual page by Alex van den Bogaerdt E<lt>alex@ergens.op.het.netE<gt>