1RRDGRAPH_DATA(1)                    rrdtool                   RRDGRAPH_DATA(1)
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NAME

6       rrdgraph_data - preparing data for graphing in rrdtool graph
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SYNOPSIS

9       DEF:<vname>=<rrdfile>:<ds-name>:<CF>[:step=<step>][:start=<time>][:end=<time>][:reduce=<CF>][:daemon=<address>]
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11       VDEF:vname=RPN expression
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13       CDEF:vname=RPN expression
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DESCRIPTION

16       These three instructions extract data values out of the RRD files,
17       optionally altering them (think, for example, of a bytes to bits
18       conversion). If so desired, you can also define variables containing
19       useful information such as maximum, minimum etcetera. Two of the
20       instructions use a language called RPN which is described in its own
21       manual page.
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23       Variable names (vname) must be made up strings of the following
24       characters "A-Z, a-z, 0-9, _, -" and a maximum length of 255
25       characters.
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27       When picking variable names, make sure you do not choose a name that is
28       already taken by an RPN operator. A safe bet is to use lowercase or
29       mixed case names for variables since operators will always be in
30       uppercase.
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DEF

33       DEF:<vname>=<rrdfile>:<ds-name>:<CF>[:step=<step>][:start=<time>][:end=<time>][:reduce=<CF>][:daemon=<address>]
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35       This command fetches data from an RRD file.  The virtual name vname can
36       then be used throughout the rest of the script. By default, an RRA
37       which contains the correct consolidated data at an appropriate
38       resolution will be chosen.  The resolution can be overridden with the
39       --step option.  The resolution can again be overridden by specifying
40       the step size.  The time span of this data is the same as for the graph
41       by default, you can override this by specifying start and end.
42       Remember to escape colons in the time specification!
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44       If the resolution of the data is higher than the resolution of the
45       graph, the data will be further consolidated. This may result in a
46       graph that spans slightly more time than requested.  Ideally each point
47       in the graph should correspond with one CDP from an RRA.  For instance,
48       if your RRD has an RRA with a resolution of 1800 seconds per CDP, you
49       should create an image with width 400 and time span 400*1800 seconds
50       (use appropriate start and end times, such as "--start
51       end-8days8hours").
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53       If consolidation needs to be done, the CF of the RRA specified in the
54       DEF itself will be used to reduce the data density. This behavior can
55       be changed using ":reduce=<CF>".  This optional parameter specifies the
56       CF to use during the data reduction phase.
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58       It is possible to request single data sources from a specific
59       RRDCacheD, see rrdcached, using the ":daemon=<address>" parameter. The
60       value given to this parameter follows the same syntax as other means to
61       specify the address of the caching daemon. It is described in detail in
62       rrdcached. Beware, however, that colons (in IPv6 addresses and as a
63       port separator, for example) need to be escaped using a backslash.
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65       Example:
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67               DEF:ds0=router.rrd:ds0:AVERAGE
68               DEF:ds0weekly=router.rrd:ds0:AVERAGE:step=7200
69               DEF:ds0weekly=router.rrd:ds0:AVERAGE:start=end-1h
70               DEF:ds0weekly=router.rrd:ds0:AVERAGE:start=11\:00:end=start+1h
71               DEF:ds0weekly=router.rrd:ds0:AVERAGE:daemon=collect1.example.com
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VDEF

74       VDEF:vname=RPN expression
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76       This command returns a value and/or a time according to the RPN
77       statements used. The resulting vname will, depending on the functions
78       used, have a value and a time component.  When you use this vname in
79       another RPN expression, you are effectively inserting its value just as
80       if you had put a number at that place.  The variable can also be used
81       in the various graph and print elements.
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83       Example: "VDEF:avg=mydata,AVERAGE"
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85       Note that currently only aggregation functions work in VDEF rpn
86       expressions.  Patches to change this are welcome.
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CDEF

89       CDEF:vname=RPN expression
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91       This command creates a new set of data points (in memory only, not in
92       the RRD file) out of one or more other data series. The RPN
93       instructions are used to evaluate a mathematical function on each data
94       point. The resulting vname can then be used further on in the script,
95       just as if it were generated by a DEF instruction.
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97       Example: "CDEF:mydatabits=mydata,8,*"
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About CDEF versus VDEF

100       At some point in processing, RRDtool has gathered an array of rates
101       ready to display.
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103       CDEF works on such an array.  For example, CDEF:new=ds0,8,* would
104       multiply each of the array members by eight (probably transforming
105       bytes into bits). The result is an array containing the new values.
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107       VDEF also works on such an array but in a different way.  For example,
108       VDEF:max=ds0,MAXIMUM would scan each of the array members and store the
109       maximum value.
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111   When do you use VDEF versus CDEF?
112       Use CDEF to transform your data prior to graphing.  In the above
113       example, we'd use a CDEF to transform bytes to bits before graphing the
114       bits.
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116       You use a VDEF if you want max(1,5,3,2,4) to return five which would be
117       displayed in the graph's legend (to answer, what was the maximum value
118       during the graph period).
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120       If you want to apply 'complex' operations to the result of a VDEF you
121       have to use a CDEF again since VDEFs only look like RPN expressions,
122       they aren't really.
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SEE ALSO

125       rrdgraph gives an overview of how rrdtool graph works.  rrdgraph_data
126       describes DEF,CDEF and VDEF in detail.  rrdgraph_rpn describes the RPN
127       language used in the ?DEF statements.  rrdgraph_graph page describes
128       all of the graph and print functions.
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130       Make sure to read rrdgraph_examples for tips&tricks.
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AUTHOR

133       Program by Tobias Oetiker <tobi@oetiker.ch>
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135       This manual page by Alex van den Bogaerdt <alex@vandenbogaerdt.nl> with
136       corrections and/or additions by several people
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1401.8.0                             2022-03-14                  RRDGRAPH_DATA(1)
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