1RRDGRAPH_DATA(1) rrdtool RRDGRAPH_DATA(1)
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6 rrdgraph_data - preparing data for graphing in rrdtool graph
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9 DEF:<vname>=<rrdfile>:<ds-name>:<CF>[:step=<step>][:start=<time>][:end=<time>][:reduce=<CF>]
10 VDEF:vname=RPN expression
12 CDEF:vname=RPN expression
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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.
22 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 characters.
25 When picking variable names, make sure you do not choose a name that is
27 already taken by an RPN operator. A safe bet it to use lowercase or
28 mixed case names for variables since operators will always be in
29 uppercase.
30
32 DEF:<vname>=<rrdfile>:<ds-name>:<CF>[:step=<step>][:start=<time>][:end=<time>][:reduce=<CF>]
33 This command fetches data from an RRD file. The virtual name vname can
35 then be used throughout the rest of the script. By default, an RRA
36 which contains the correct consolidated data at an appropriate
37 resolution will be chosen. The resolution can be overridden with the
38 --step option. The resolution can again be overridden by specifying
39 the step size. The time span of this data is the same as for the graph
40 by default, you can override this by specifying start and end.
41 Remember to escape colons in the time specification!
42 If the resolution of the data is higher than the resolution of the
44 graph, the data will be further consolidated. This may result in a
45 graph that spans slightly more time than requested. Ideally each point
46 in the graph should correspond with one CDP from an RRA. For instance,
47 if your RRD has an RRA with a resolution of 1800 seconds per CDP, you
48 should create an image with width 400 and time span 400*1800 seconds
49 (use appropriate start and end times, such as "--start
50 end-8days8hours").
51 If consolidation needs to be done, the CF of the RRA specified in the
53 DEF itself will be used to reduce the data density. This behavior can
54 be changed using ":reduce=<CF>". This optional parameter specifies the
55 CF to use during the data reduction phase.
56 Example:
58 DEF:ds0=router.rrd:ds0:AVERAGE
60 DEF:ds0weekly=router.rrd:ds0:AVERAGE:step=7200
61 DEF:ds0weekly=router.rrd:ds0:AVERAGE:start=end-1h
62 DEF:ds0weekly=router.rrd:ds0:AVERAGE:start=11\:00:end=start+1h
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65 VDEF:vname=RPN expression
66 This command returns a value and/or a time according to the RPN
68 statements used. The resulting vname will, depending on the functions
69 used, have a value and a time component. When you use this vname in
70 another RPN expression, you are effectively inserting its value just as
71 if you had put a number at that place. The variable can also be used
72 in the various graph and print elements.
73 Example: "VDEF:avg=mydata,AVERAGE"
75 Note that currently only aggregation functions work in VDEF rpn
77 expressions. Patches to change this are welcome.
78
80 CDEF:vname=RPN expression
81 This command creates a new set of data points (in memory only, not in
83 the RRD file) out of one or more other data series. The RPN
84 instructions are used to evaluate a mathematical function on each data
85 point. The resulting vname can then be used further on in the script,
86 just as if it were generated by a DEF instruction.
87 Example: "CDEF:mydatabits=mydata,8,*"
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91 At some point in processing, RRDtool has gathered an array of rates
92 ready to display.
93 CDEF works on such an array. For example, CDEF:new=ds0,8,* would
95 multiply each of the array members by eight (probably transforming
96 bytes into bits). The result is an array containing the new values.
97 VDEF also works on such an array but in a different way. For example,
99 VDEF:max=ds0,MAXIMUM would scan each of the array members and store the
100 maximum value.
101 When do you use VDEF versus CDEF?
103 Use CDEF to transform your data prior to graphing. In the above
104 example, we'd use a CDEF to transform bytes to bits before graphing the
105 bits.
106 You use a VDEF if you want max(1,5,3,2,4) to return five which would be
108 displayed in the graph's legend (to answer, what was the maximum value
109 during the graph period).
110 If you want to apply 'complex' operations to the result of a VDEF you
112 have to use a CDEF again since VDEFs only look like RPN expressions,
113 they aren't really.
114
116 rrdgraph gives an overview of how rrdtool graph works. rrdgraph_data
117 describes DEF,CDEF and VDEF in detail. rrdgraph_rpn describes the RPN
118 language used in the ?DEF statements. rrdgraph_graph page describes
119 all of the graph and print functions.
120 Make sure to read rrdgraph_examples for tips&tricks.
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124 Program by Tobias Oetiker <tobi@oetiker.ch>
125 This manual page by Alex van den Bogaerdt <alex@vandenbogaerdt.nl> with
127 corrections and/or additions by several people
1281.4.8 2013-05-23 RRDGRAPH_DATA(1)