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<ul>
<li><a href="#name">NAME</a></li>
<li><a href="#synopsis">SYNOPSIS</a></li>
<li><a href="#description">DESCRIPTION</a></li>
<li><a href="#def">DEF</a></li>
<li><a href="#vdef">VDEF</a></li>
<li><a href="#cdef">CDEF</a></li>
<li><a href="#about_cdef_versus_vdef">About CDEF versus VDEF</a></li>
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<li><a href="#when_do_you_use_vdef_versus_cdef">When do you use <strong>VDEF</strong> versus <strong>CDEF</strong>?</a></li>
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<li><a href="#see_also">SEE ALSO</a></li>
<li><a href="#author">AUTHOR</a></li>
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<p>
</p>
<h1><a name="name">NAME</a></h1>
<p>rrdgraph_data - preparing data for graphing in rrdtool graph</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<p><strong>DEF:</strong><em><vname></em>=<em><rrdfile></em>:<em><ds-name></em>:<em><CF></em>[:step=<em><step></em>][:start=<em><time></em>][:end=<em><time></em>][:reduce=<em><<strong>CF</strong>></em>]</p>
<p><strong>VDEF</strong>:<em>vname</em>=<em>RPN expression</em></p>
<p><strong>CDEF</strong>:<em>vname</em>=<em>RPN expression</em></p>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p>These three instructions extract data values out of the <strong>RRD</strong> 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 <strong>RPN</strong> which is described in its
own manual page.</p>
<p>Variable names (<em>vname</em>) must be made up strings of the following characters
<code>A-Z, a-z, 0-9, -,_</code> and a maximum length of 255 characters.</p>
<p>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.</p>
<p>
</p>
<hr />
<h1><a name="def">DEF</a></h1>
<p><strong>DEF:</strong><em><vname></em>=<em><rrdfile></em>:<em><ds-name></em>:<em><CF></em>[:step=<em><step></em>][:start=<em><time></em>][:end=<em><time></em>][:reduce=<em><<strong>CF</strong>></em>]</p>
<p>This command fetches data from an <strong>RRD</strong> file. The virtual name
<em>vname</em> can then be used throughout the rest of the script. By
default, an <strong>RRA</strong> which contains the correct consolidated data
at an appropriate resolution will be chosen. The resolution can
be overridden with the <a href="././rrdgraph.html#item_time">--step</a> option.
The resolution can again be overridden by specifying the <strong>step size</strong>.
The time span of this data is the same as for the graph by default,
you can override this by specifying <strong>start and end</strong>. Remember to
escape colons in the time specification!</p>
<p>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 <strong>CDP</strong>
from an <strong>RRA</strong>. For instance, if your <strong>RRD</strong> has an <strong>RRA</strong> with
a resolution of 1800 seconds per <strong>CDP</strong>, you should create an
image with width 400 and time span 400*1800 seconds (use appropriate
start and end times, such as <code>--start end-8days8hours</code>).</p>
<p>If consolidation needs to be done, the <strong>CF</strong> of the <strong>RRA</strong> specified in the
<strong>DEF</strong> itself will be used to reduce the data density. This behaviour can
be changed using <code>:reduce=<CF></code>. This optional parameter
specifies the <strong>CF</strong> to use during the data reduction phase.</p>
<p>Example:</p>
<pre>
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</pre>
<p>
</p>
<hr />
<h1><a name="vdef">VDEF</a></h1>
<p><strong>VDEF</strong>:<em>vname</em>=<em>RPN expression</em></p>
<p>This command returns a value and/or a time according to the <strong>RPN</strong>
statements used. The resulting <em>vname</em> will, depending on the
functions used, have a value and a time component. When you use
this <em>vname</em> in another <strong>RPN</strong> 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.</p>
<p>Example: <code>VDEF:avg=mydata,AVERAGE</code></p>
<p>Note that currently only aggregation functions work in VDEF rpn expressions.
Patches to change this are welcome.</p>
<p>
</p>
<hr />
<h1><a name="cdef">CDEF</a></h1>
<p><strong>CDEF</strong>:<em>vname</em>=<em>RPN expression</em></p>
<p>This command creates a new set of data points (in memory only, not
in the <strong>RRD</strong> file) out of one or more other data series. The <strong>RPN</strong>
instructions are used to evaluate a mathematical function on each
data point. The resulting <em>vname</em> can then be used further on in
the script, just as if it were generated by a <strong>DEF</strong> instruction.</p>
<p>Example: <code>CDEF:mydatabits=mydata,8,*</code></p>
<p>
</p>
<hr />
<h1><a name="about_cdef_versus_vdef">About CDEF versus VDEF</a></h1>
<p>At some point in processing, <strong>RRDtool</strong> has gathered an array of rates
ready to display.</p>
<p><strong>CDEF</strong> works on such an array. For example, <em>CDEF:new=ds0,8,*</em>
would multiply each of the array members by eight (probably
transforming bytes into bits). The result is an array containing the
new values.</p>
<p><strong>VDEF</strong> also works on such an array but in a different way. For
example, <em>VDEF:max=ds0,MAXIMUM</em> would scan each of the array members
and store the maximum value.</p>
<p>
</p>
<h2><a name="when_do_you_use_vdef_versus_cdef">When do you use <strong>VDEF</strong> versus <strong>CDEF</strong>?</a></h2>
<p>Use <strong>CDEF</strong> to transform your data prior to graphing. In the above
example, we'd use a <strong>CDEF</strong> to transform bytes to bits before
graphing the bits.</p>
<p>You use a <strong>VDEF</strong> if you want <em>max(1,5,3,2,4)</em> to return five which
would be displayed in the graph's legend (to answer, what was the
maximum value during the graph period).</p>
<p>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
realy.</p>
<p>
</p>
<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<p><a href="././rrdgraph.html">the rrdgraph manpage</a> gives an overview of how <strong>rrdtool graph</strong> works.
<a href="././rrdgraph_data.html">the rrdgraph_data manpage</a> describes <strong>DEF</strong>,<strong>CDEF</strong> and <strong>VDEF</strong> in detail.
<a href="././rrdgraph_rpn.html">the rrdgraph_rpn manpage</a> describes the <strong>RPN</strong> language used in the <strong>?DEF</strong> statements.
<a href="././rrdgraph_graph.html">the rrdgraph_graph manpage</a> page describes all of the graph and print functions.</p>
<p>Make sure to read <a href="././rrdgraph_examples.html">the rrdgraph_examples manpage</a> for tips&tricks.</p>
<p>
</p>
<hr />
<h1><a name="author">AUTHOR</a></h1>
<p>Program by Tobias Oetiker <<a href="mailto:tobi@oetiker.ch">tobi@oetiker.ch</a>></p>
<p>This manual page by Alex van den Bogaerdt <<a href="mailto:alex@vandenbogaerdt.nl">alex@vandenbogaerdt.nl</a>>
with corrections and/or additions by several people</p>
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