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170 lines
8 KiB
HTML
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<title>rrdgraph_data</title>
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<meta http-equiv="content-type" content="text/html; charset=utf-8" />
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<link rev="made" href="mailto:root@localhost" />
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<body style="background-color: white">
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<!-- INDEX BEGIN -->
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<p><a name="__index__"></a></p>
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<!--
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<ul>
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<li><a href="#name">NAME</a></li>
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<li><a href="#synopsis">SYNOPSIS</a></li>
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<li><a href="#description">DESCRIPTION</a></li>
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<li><a href="#def">DEF</a></li>
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<li><a href="#vdef">VDEF</a></li>
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<li><a href="#cdef">CDEF</a></li>
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<li><a href="#about_cdef_versus_vdef">About CDEF versus VDEF</a></li>
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<ul>
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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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</ul>
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<li><a href="#see_also">SEE ALSO</a></li>
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<li><a href="#author">AUTHOR</a></li>
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</ul>
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<!-- INDEX END -->
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<p>
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</p>
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<h1><a name="name">NAME</a></h1>
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<p>rrdgraph_data - preparing data for graphing in rrdtool graph</p>
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<p>
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</p>
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<hr />
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<h1><a name="synopsis">SYNOPSIS</a></h1>
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<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>
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<p><strong>VDEF</strong>:<em>vname</em>=<em>RPN expression</em></p>
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<p><strong>CDEF</strong>:<em>vname</em>=<em>RPN expression</em></p>
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<p>
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</p>
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<hr />
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<h1><a name="description">DESCRIPTION</a></h1>
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<p>These three instructions extract data values out of the <strong>RRD</strong> files,
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optionally altering them (think, for example, of a bytes to bits
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conversion). If so desired, you can also define variables containing
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useful information such as maximum, minimum etcetera. Two of the
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instructions use a language called <strong>RPN</strong> which is described in its
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own manual page.</p>
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<p>Variable names (<em>vname</em>) must be made up strings of the following characters
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<code>A-Z, a-z, 0-9, -,_</code> and a maximum length of 255 characters.</p>
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<p>When picking variable names, make sure you do not choose a name that is
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already taken by an RPN operator. A safe bet it to use lowercase or
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mixed case names for variables since operators will always be in uppercase.</p>
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<p>
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</p>
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<hr />
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<h1><a name="def">DEF</a></h1>
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<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>
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<p>This command fetches data from an <strong>RRD</strong> file. The virtual name
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<em>vname</em> can then be used throughout the rest of the script. By
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default, an <strong>RRA</strong> which contains the correct consolidated data
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at an appropriate resolution will be chosen. The resolution can
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be overridden with the <a href="././rrdgraph.html#item_time">--step</a> option.
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The resolution can again be overridden by specifying the <strong>step size</strong>.
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The time span of this data is the same as for the graph by default,
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you can override this by specifying <strong>start and end</strong>. Remember to
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escape colons in the time specification!</p>
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<p>If the resolution of the data is higher than the resolution of the
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graph, the data will be further consolidated. This may result in
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a graph that spans slightly more time than requested.
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Ideally each point in the graph should correspond with one <strong>CDP</strong>
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from an <strong>RRA</strong>. For instance, if your <strong>RRD</strong> has an <strong>RRA</strong> with
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a resolution of 1800 seconds per <strong>CDP</strong>, you should create an
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image with width 400 and time span 400*1800 seconds (use appropriate
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start and end times, such as <code>--start end-8days8hours</code>).</p>
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<p>If consolidation needs to be done, the <strong>CF</strong> of the <strong>RRA</strong> specified in the
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<strong>DEF</strong> itself will be used to reduce the data density. This behavior can
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be changed using <code>:reduce=<CF></code>. This optional parameter
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specifies the <strong>CF</strong> to use during the data reduction phase.</p>
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<p>Example:</p>
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<pre>
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DEF:ds0=router.rrd:ds0:AVERAGE
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DEF:ds0weekly=router.rrd:ds0:AVERAGE:step=7200
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DEF:ds0weekly=router.rrd:ds0:AVERAGE:start=end-1h
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DEF:ds0weekly=router.rrd:ds0:AVERAGE:start=11\:00:end=start+1h</pre>
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<p>
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</p>
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<hr />
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<h1><a name="vdef">VDEF</a></h1>
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<p><strong>VDEF</strong>:<em>vname</em>=<em>RPN expression</em></p>
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<p>This command returns a value and/or a time according to the <strong>RPN</strong>
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statements used. The resulting <em>vname</em> will, depending on the
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functions used, have a value and a time component. When you use
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this <em>vname</em> in another <strong>RPN</strong> expression, you are effectively
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inserting its value just as if you had put a number at that place.
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The variable can also be used in the various graph and print
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elements.</p>
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<p>Example: <code>VDEF:avg=mydata,AVERAGE</code></p>
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<p>Note that currently only aggregation functions work in VDEF rpn expressions.
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Patches to change this are welcome.</p>
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<p>
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</p>
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<hr />
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<h1><a name="cdef">CDEF</a></h1>
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<p><strong>CDEF</strong>:<em>vname</em>=<em>RPN expression</em></p>
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<p>This command creates a new set of data points (in memory only, not
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in the <strong>RRD</strong> file) out of one or more other data series. The <strong>RPN</strong>
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instructions are used to evaluate a mathematical function on each
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data point. The resulting <em>vname</em> can then be used further on in
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the script, just as if it were generated by a <strong>DEF</strong> instruction.</p>
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<p>Example: <code>CDEF:mydatabits=mydata,8,*</code></p>
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<p>
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</p>
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<hr />
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<h1><a name="about_cdef_versus_vdef">About CDEF versus VDEF</a></h1>
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<p>At some point in processing, <strong>RRDtool</strong> has gathered an array of rates
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ready to display.</p>
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<p><strong>CDEF</strong> works on such an array. For example, <em>CDEF:new=ds0,8,*</em>
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would multiply each of the array members by eight (probably
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transforming bytes into bits). The result is an array containing the
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new values.</p>
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<p><strong>VDEF</strong> also works on such an array but in a different way. For
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example, <em>VDEF:max=ds0,MAXIMUM</em> would scan each of the array members
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and store the maximum value.</p>
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<p>
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</p>
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<h2><a name="when_do_you_use_vdef_versus_cdef">When do you use <strong>VDEF</strong> versus <strong>CDEF</strong>?</a></h2>
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<p>Use <strong>CDEF</strong> to transform your data prior to graphing. In the above
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example, we'd use a <strong>CDEF</strong> to transform bytes to bits before
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graphing the bits.</p>
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<p>You use a <strong>VDEF</strong> if you want <em>max(1,5,3,2,4)</em> to return five which
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would be displayed in the graph's legend (to answer, what was the
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maximum value during the graph period).</p>
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<p>If you want to apply 'complex' operations to the result of a VDEF you have
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to use a CDEF again since VDEFs only look like RPN expressions, they aren't
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really.</p>
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<p>
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</p>
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<hr />
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<h1><a name="see_also">SEE ALSO</a></h1>
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<p><a href="././rrdgraph.html">the rrdgraph manpage</a> gives an overview of how <strong>rrdtool graph</strong> works.
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<a href="././rrdgraph_data.html">the rrdgraph_data manpage</a> describes <strong>DEF</strong>,<strong>CDEF</strong> and <strong>VDEF</strong> in detail.
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<a href="././rrdgraph_rpn.html">the rrdgraph_rpn manpage</a> describes the <strong>RPN</strong> language used in the <strong>?DEF</strong> statements.
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<a href="././rrdgraph_graph.html">the rrdgraph_graph manpage</a> page describes all of the graph and print functions.</p>
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<p>Make sure to read <a href="././rrdgraph_examples.html">the rrdgraph_examples manpage</a> for tips&tricks.</p>
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<p>
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</p>
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<hr />
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<h1><a name="author">AUTHOR</a></h1>
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<p>Program by Tobias Oetiker <<a href="mailto:tobi@oetiker.ch">tobi@oetiker.ch</a>></p>
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<p>This manual page by Alex van den Bogaerdt <<a href="mailto:alex@vandenbogaerdt.nl">alex@vandenbogaerdt.nl</a>>
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with corrections and/or additions by several people</p>
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</body>
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</html>
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