Rather than calling "FLUSH" for each RRD file needed for drawing a

[rrdtool.git] / doc / rrdgraph_data.pod

diff --git a/doc/rrdgraph_data.pod b/doc/rrdgraph_data.pod
index 6c8b28a..57b9d0a 100644 (file)
--- a/doc/rrdgraph_data.pod
+++ b/doc/rrdgraph_data.pod
@@ -4,7 +4,7 @@ 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<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>>][:daemon=I<E<lt>addressE<gt>>]
 
 B<VDEF>:I<vname>=I<RPN expression>
 
@@ -23,12 +23,12 @@ 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 save bet it to use lowercase or
-mixedcase names for variables since operators will always be in uppercase.
+already taken by an RPN operator. A safe bet it to use lowercase or
+mixed case 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>>]
+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>>][:daemon=I<E<lt>addressE<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
@@ -50,16 +50,24 @@ 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
+B<DEF> itself will be used to reduce the data density. This behavior 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.
 
+It is possible to request single data sources from a specific I<RRDCacheD>, see
+L<rrdcached(1)>, using the C<:daemon=I<E<lt>addressE<gt>>> parameter. The
+value given to this parameter follows the same syntax as other means to specify
+the address of the caching daemon. It is described in detail in the
+L<rrdcached(1)> manual page. Beware, however, that colons (in IPv6 addresses
+and as a port separator, for example) need to be escaped using a backslash.
+
 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
+        DEF:ds0weekly=router.rrd:ds0:AVERAGE:daemon=collect1.example.com
 
 =head1 VDEF
 
@@ -75,7 +83,7 @@ elements.
 
 Example: C<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.
 
 =head1 CDEF
@@ -90,6 +98,34 @@ the script, just as if it were generated by a B<DEF> instruction.
 
 Example: C<CDEF:mydatabits=mydata,8,*>
 
+=head1 About CDEF versus VDEF
+
+At some point in processing, B<RRDtool> has gathered an array of rates
+ready to display.
+
+B<CDEF> works on such an array.  For example, I<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.
+
+B<VDEF> also works on such an array but in a different way.  For
+example, I<VDEF:max=ds0,MAXIMUM> would scan each of the array members
+and store the maximum value.
+
+=head2 When do you use B<VDEF> versus B<CDEF>?  
+
+Use B<CDEF> to transform your data prior to graphing.  In the above
+example, we'd use a B<CDEF> to transform bytes to bits before
+graphing the bits.
+
+You use a B<VDEF> if you want I<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
+really.
+
 =head1 SEE ALSO
 
 L<rrdgraph> gives an overview of how B<rrdtool graph> works.
@@ -103,4 +139,5 @@ Make sure to read L<rrdgraph_examples> for tipsE<amp>tricks.
 
 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>
+This manual page by Alex van den Bogaerdt E<lt>alex@vandenbogaerdt.nlE<gt>
+with corrections and/or additions by several people