1 RRDGRAPH_RPN(1) rrdtool RRDGRAPH_RPN(1)
6 rrdgraph_rpn - About RPN Math in rrdtool graph
9 _\bR_\bP_\bN _\be_\bx_\bp_\br_\be_\bs_\bs_\bi_\bo_\bn:=_\bv_\bn_\ba_\bm_\be|_\bo_\bp_\be_\br_\ba_\bt_\bo_\br|_\bv_\ba_\bl_\bu_\be[,_\bR_\bP_\bN _\be_\bx_\bp_\br_\be_\bs_\bs_\bi_\bo_\bn]
14 stack and push your data onto this stack. Whenever you execute an
15 operation, it takes as many elements from the stack as needed. Pushing
16 is done implicitly, so whenever you specify a number or a variable, it
17 gets pushed onto the stack automatically.
19 At the end of the calculation there should be one and only one value
20 left on the stack. This is the outcome of the function and this is
24 only support a limited list of functions.
26 Example: "VDEF:maximum=mydata,MAXIMUM"
28 This will set variable "maximum" which you now can use in the rest of
29 your RRD script.
31 Example: "CDEF:mydatabits=mydata,8,*"
34 operator _\b*. The operator needs two elements and uses those to return
35 one value. This value is then stored in _\bm_\by_\bd_\ba_\bt_\ba_\bb_\bi_\bt_\bs. As you may have
36 guessed, this instruction means nothing more than _\bm_\by_\bd_\ba_\bt_\ba_\bb_\bi_\bt_\bs _\b= _\bm_\by_\bd_\ba_\bt_\ba _\b*
38 which order to process the input. For expressions like "a = b + 3 * 5"
40 with parentheses you could change this order: "a = (b + 3) * 5". In
44 Boolean operators
47 Pop two elements from the stack, compare them for the selected
48 condition and return 1 for true or 0 for false. Comparing an
49 _\bu_\bn_\bk_\bn_\bo_\bw_\bn or an _\bi_\bn_\bf_\bi_\bn_\bi_\bt_\be value will result in _\bu_\bn_\bk_\bn_\bo_\bw_\bn returned ...
55 respectively to _\bp_\bo_\bs_\bi_\bt_\bi_\bv_\be _\bo_\br _\bn_\be_\bg_\ba_\bt_\bi_\bv_\be _\bi_\bn_\bf_\bi_\bn_\bi_\bt_\by. Returns 1 for true
56 or 0 for false.
60 Pops three elements from the stack. If the element popped last is
61 0 (false), the value popped first is pushed back onto the stack,
62 otherwise the value popped second is pushed back. This does,
63 indeed, mean that any value other than 0 is considered to be true.
65 Example: "A,B,C,IF" should be read as "if (A) then (B) else (C)"
69 Comparing values
72 Pops two elements from the stack and returns the smaller or larger,
79 Pops two elements from the stack and uses them to define a range.
80 Then it pops another element and if it falls inside the range, it
83 The range defined includes the two boundaries (so: a number equal
84 to one of the boundaries will be pushed back). If any of the three
85 numbers involved is either _\bu_\bn_\bk_\bn_\bo_\bw_\bn or _\bi_\bn_\bf_\bi_\bn_\bi_\bt_\be this function will
89 lower than 0 or if it is higher than 100.
93 Arithmetics
96 Add, subtract, multiply, divide, modulo
100 NAN-safe addition. If one parameter is NAN/UNKNOWN it'll be treated
101 as zero. If both parameters are NAN/UNKNOWN, NAN/UNKNOWN will be
102 returned.
106 Sine and cosine (input in radians), log and exp (natural
107 logarithm), square root.
111 Arctangent (output in radians).
115 Arctangent of y,x components (output in radians). This pops one
116 element from the stack, the x (cosine) component, and then a
117 second, which is the y (sine) component. It then pushes the
118 arctangent of their ratio, resolving the ambiguity between
119 quadrants.
121 Example: "CDEF:angle=Y,X,ATAN2,RAD2DEG" will convert "X,Y"
122 components into an angle in degrees.
126 Round down or up to the nearest integer.
130 Convert angle in degrees to radians, or radians to degrees.
134 Take the absolute value.
136 Set Operations
141 then sorted (or reversed) in place on the stack.
143 Example: "CDEF:x=v1,v2,v3,v4,v5,v6,6,SORT,POP,5,REV,POP,+,+,+,4,/"
144 will compute the average of the values v1 to v6 after removing the
145 smallest and largest.
149 Pop one element (_\bc_\bo_\bu_\bn_\bt) from the stack. Now pop _\bc_\bo_\bu_\bn_\bt elements and
150 build the average, ignoring all UNKNOWN values in the process.
152 Example: "CDEF:x=a,b,c,d,4,AVG"
156 Create a "sliding window" average of another data series.
158 Usage: CDEF:smoothed=x,1800,TREND
160 This will create a half-hour (1800 second) sliding window average
161 of x. The average is essentially computed as shown here:
163 +---!---!---!---!---!---!---!---!--->
164 now
165 delay t0
166 <--------------->
167 delay t1
168 <--------------->
169 delay t2
170 <--------------->
173 Value at sample (t0) will be the average between (t0-delay) and (t0)
174 Value at sample (t1) will be the average between (t1-delay) and (t1)
175 Value at sample (t2) will be the average between (t2-delay) and (t2)
177 TRENDNAN is - in contrast to TREND - NAN-safe. If you use TREND and
178 one source value is NAN the complete sliding window is affected.
179 The TRENDNAN operation ignores all NAN-values in a sliding window
180 and computes the average of the remaining values.
184 Create a "sliding window" average/sigma of another data series,
185 that also shifts the data series by given amounts of of time as
186 well
188 Usage - explicit stating shifts: CDEF:predict=<shift n>,...,<shift
189 1>,n,<window>,x,PREDICT CDEF:sigma=<shift n>,...,<shift
190 1>,n,<window>,x,PREDICTSIGMA
192 Usage - shifts defined as a base shift and a number of time this is
193 applied CDEF:predict=<shift multiplier>,-n,<window>,x,PREDICT
194 CDEF:sigma=<shift multiplier>,-n,<window>,x,PREDICTSIGMA
196 Example: CDEF:predict=172800,86400,2,1800,x,PREDICT
198 This will create a half-hour (1800 second) sliding window
199 average/sigma of x, that average is essentially computed as shown
200 here:
202 +---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!--->
203 now
204 shift 1 t0
205 <----------------------->
206 window
207 <--------------->
208 shift 2
209 <----------------------------------------------->
210 window
211 <--------------->
212 shift 1 t1
213 <----------------------->
214 window
215 <--------------->
216 shift 2
217 <----------------------------------------------->
218 window
219 <--------------->
221 Value at sample (t0) will be the average between (t0-shift1-window) and (t0-shift1)
222 and between (t0-shift2-window) and (t0-shift2)
223 Value at sample (t1) will be the average between (t1-shift1-window) and (t1-shift1)
224 and between (t1-shift2-window) and (t1-shift2)
226 The function is by design NAN-safe. This also allows for
227 extrapolation into the future (say a few days) - you may need to
228 define the data series whit the optional start= parameter, so that
229 the source data series has enough data to provide prediction also
230 at the beginning of a graph...
232 Here an example, that will create a 10 day graph that also shows
233 the prediction 3 days into the future with its uncertainty value
234 (as defined by avg+-4*sigma) This also shows if the prediction is
235 exceeded at a certain point.
237 rrdtool graph image.png --imgformat=PNG \
238 --start=-7days --end=+3days --width=1000 --height=200
239 --alt-autoscale-max \
240 DEF:value=value.rrd:value:AVERAGE:start=-14days \
241 LINE1:value#ff0000:value \
242 CDEF:predict=86400,-7,1800,value,PREDICT \
243 CDEF:sigma=86400,-7,1800,value,PREDICTSIGMA \
244 CDEF:upper=predict,sigma,3,*,+ \
245 CDEF:lower=predict,sigma,3,*,- \
246 LINE1:predict#00ff00:prediction \
247 LINE1:upper#0000ff:upper\ certainty\ limit \
248 LINE1:lower#0000ff:lower\ certainty\ limit \
249 CDEF:exceeds=value,UN,0,value,lower,upper,LIMIT,UN,IF \
250 TICK:exceeds#aa000080:1
252 Note: Experience has shown that a factor between 3 and 5 to scale
253 sigma is a good discriminator to detect abnormal behavior. This
254 obviously depends also on the type of data and how "noisy" the data
255 series is.
257 This prediction can only be used for short term extrapolations -
258 say a few days into the future-
260 Special values
263 Pushes an unknown value on the stack
267 Pushes a positive or negative infinite value on the stack. When
268 such a value is graphed, it appears at the top or bottom of the
269 graph, no matter what the actual value on the y-axis is.
275 allows you to do calculations across the data. This function
281 otherwise the result of the vname variable at the previous time
282 step. This allows you to do calculations across the data. This
287 Pushes the number 1 if this is the first value of the data set, the
288 number 2 if it is the second, and so on. This special value allows
289 you to make calculations based on the position of the value within
292 Time
293 Time inside RRDtool is measured in seconds since the epoch. The
294 epoch is defined to be "Thu Jan 1 00:00:00 UTC 1970".
298 Pushes the current time on the stack.
302 Pushes the time the currently processed value was taken at onto the
303 stack.
308 valid at that time including daylight saving time if your OS
309 supports it, and pushes the result on the stack. There is an
310 elaborate example in the examples section below on how to use this.
312 Processing the stack directly
315 Duplicate the top element, remove the top element, exchange the two
316 top elements.
324 MAXIMUM, MINIMUM, AVERAGE
325 Return the corresponding value, MAXIMUM and MINIMUM also return the
326 first occurrence of that value in the time component.
328 Example: "VDEF:avg=mydata,AVERAGE"
330 STDEV
331 Returns the standard deviation of the values.
333 Example: "VDEF:stdev=mydata,STDEV"
335 LAST, FIRST
336 Return the last/first non-nan or infinite value for the selected
337 data stream, including its timestamp.
339 Example: "VDEF:first=mydata,FIRST"
341 TOTAL
342 Returns the rate from each defined time slot multiplied with the
343 step size. This can, for instance, return total bytes transferred
344 when you have logged bytes per second. The time component returns
345 the number of seconds.
347 Example: "VDEF:total=mydata,TOTAL"
349 PERCENT, PERCENTNAN
350 This should follow a D\bDE\bEF\bF or C\bCD\bDE\bEF\bF _\bv_\bn_\ba_\bm_\be. The _\bv_\bn_\ba_\bm_\be is popped,
351 another number is popped which is a certain percentage (0..100).
352 The data set is then sorted and the value returned is chosen such
359 (NaN < -INF < finite values < INF)
361 Example: "VDEF:perc95=mydata,95,PERCENT"
362 "VDEF:percnan95=mydata,95,PERCENTNAN"
364 LSLSLOPE, LSLINT, LSLCORREL
365 Return the parameters for a L\bLeast S\bSquares L\bLine _\b(_\by _\b= _\bm_\bx _\b+_\bb_\b) which
367 line related to the COUNT position of the data. LSLINT is the
369 the graph. LSLCORREL is the Correlation Coefficient (also know as
370 Pearson's Product Moment Correlation Coefficient). It will range
371 from 0 to +/-1 and represents the quality of fit for the
372 approximation.
374 Example: "VDEF:slope=mydata,LSLSLOPE"
377 rrdgraph gives an overview of how r\brr\brd\bdt\bto\boo\bol\bl g\bgr\bra\bap\bph\bh works. rrdgraph_data
378 describes D\bDE\bEF\bF,C\bCD\bDE\bEF\bF and V\bVD\bDE\bEF\bF in detail. rrdgraph_rpn describes the R\bRP\bPN\bN
380 all of the graph and print functions.
382 Make sure to read rrdgraph_examples for tips&tricks.
385 Program by Tobias Oetiker <tobi@oetiker.ch>
387 This manual page by Alex van den Bogaerdt <alex@vandenbogaerdt.nl> with
388 corrections and/or additions by several people
392 1.4.8 2013-05-23 RRDGRAPH_RPN(1)