X-Git-Url: https://git.octo.it/?p=rrdtool.git;a=blobdiff_plain;f=doc%2Frrdgraph_rpn.pod;h=5558c224b70c8e15bb3455911ebeb77158695abe;hp=dfc9a0bda903e77d6538fa7cffe38eb079a4376e;hb=3b8e10c66bfeb447e8b06b7296f748c405c8453d;hpb=81ed9c86d4042e31e147b53bf14da233b6524021 diff --git a/doc/rrdgraph_rpn.pod b/doc/rrdgraph_rpn.pod index dfc9a0b..5558c22 100644 --- a/doc/rrdgraph_rpn.pod +++ b/doc/rrdgraph_rpn.pod @@ -9,7 +9,8 @@ I:=I|I|I[,I] =head1 DESCRIPTION If you have ever used a traditional HP calculator you already know -B. The idea behind B is that you have a stack and push +B (Reverse Polish Notation). +The idea behind B is that you have a stack and push your data onto this stack. Whenever you execute an operation, it takes as many elements from the stack as needed. Pushing is done implicitly, so whenever you specify a number or a variable, it gets @@ -30,7 +31,7 @@ of your RRD script. Example: C This means: push variable I, push the number 8, execute -the operator I<+>. The operator needs two elements and uses those +the operator I<*>. The operator needs two elements and uses those to return one value. This value is then stored in I. As you may have guessed, this instruction means nothing more than I. The real power of B lies in the @@ -50,7 +51,8 @@ B Pop two elements from the stack, compare them for the selected condition and return 1 for true or 0 for false. Comparing an I or an -I value will always result in 0 (false). +I value will result in I returned ... which will also be +treated as false by the B call. B @@ -99,6 +101,11 @@ B<+, -, *, /, %> Add, subtract, multiply, divide, modulo +B + +NAN-safe addition. If one parameter is NAN/UNKNOWN it'll be treated as +zero. If both parameters are NAN/UNKNOWN, NAN/UNKNOWN will be returned. + B Sine and cosine (input in radians), log and exp (natural logarithm), @@ -127,6 +134,10 @@ B Convert angle in degrees to radians, or radians to degrees. +B + +Take the absolute value. + =item Set Operations B @@ -139,7 +150,14 @@ Example: C will compute the average of the values v1 to v6 after removing the smallest and largest. -B +B + +Pop one element (I) from the stack. Now pop I elements and build the +average, ignoring all UNKNOWN values in the process. + +Example: C + +B Create a "sliding window" average of another data series. @@ -163,6 +181,84 @@ average is essentially computed as shown here: Value at sample (t1) will be the average between (t1-delay) and (t1) Value at sample (t2) will be the average between (t2-delay) and (t2) +TRENDNAN is - in contrast to TREND - NAN-safe. If you use TREND and one +source value is NAN the complete sliding window is affected. The TRENDNAN +operation ignores all NAN-values in a sliding window and computes the +average of the remaining values. + +B + +Create a "sliding window" average/sigma of another data series, that also +shifts the data series by given amounts of of time as well + +Usage - explicit stating shifts: +CDEF:predict=,...,,n,,x,PREDICT +CDEF:sigma=,...,,n,,x,PREDICTSIGMA + +Usage - shifts defined as a base shift and a number of time this is applied +CDEF:predict=,-n,,x,PREDICT +CDEF:sigma=,-n,,x,PREDICTSIGMA + +Example: +CDEF:predict=172800,86400,2,1800,x,PREDICT + +This will create a half-hour (1800 second) sliding window average/sigma of x, that +average is essentially computed as shown here: + + +---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---!---> + now + shift 1 t0 + <-----------------------> + window + <---------------> + shift 2 + <-----------------------------------------------> + window + <---------------> + shift 1 t1 + <-----------------------> + window + <---------------> + shift 2 + <-----------------------------------------------> + window + <---------------> + + Value at sample (t0) will be the average between (t0-shift1-window) and (t0-shift1) + and between (t0-shift2-window) and (t0-shift2) + Value at sample (t1) will be the average between (t1-shift1-window) and (t1-shift1) + and between (t1-shift2-window) and (t1-shift2) + + +The function is by design NAN-safe. +This also allows for extrapolation into the future (say a few days) +- you may need to define the data series whit the optional start= parameter, so that +the source data series has enough data to provide prediction also at the beginning of a graph... + +Here an example, that will create a 10 day graph that also shows the +prediction 3 days into the future with its uncertainty value (as defined by avg+-4*sigma) +This also shows if the prediction is exceeded at a certain point. + +rrdtool graph image.png --imgformat=PNG \ + --start=-7days --end=+3days --width=1000 --height=200 --alt-autoscale-max \ + DEF:value=value.rrd:value:AVERAGE:start=-14days \ + LINE1:value#ff0000:value \ + CDEF:predict=86400,-7,1800,value,PREDICT \ + CDEF:sigma=86400,-7,1800,value,PREDICTSIGMA \ + CDEF:upper=predict,sigma,3,*,+ \ + CDEF:lower=predict,sigma,3,*,- \ + LINE1:predict#00ff00:prediction \ + LINE1:upper#0000ff:upper\ certainty\ limit \ + LINE1:lower#0000ff:lower\ certainty\ limit \ + CDEF:exceeds=value,UN,0,value,lower,upper,LIMIT,UN,IF \ + TICK:exceeds#aa000080:1 + +Note: Experience has shown that a factor between 3 and 5 to scale sigma is a good +discriminator to detect abnormal behavior. This obviously depends also on the type +of data and how "noisy" the data series is. + +This prediction can only be used for short term extrapolations - say a few days into the future- + =item Special values B @@ -240,6 +336,12 @@ the first occurrence of that value in the time component. Example: C +=item STDEV + +Returns the standard deviation of the values. + +Example: C + =item LAST, FIRST Return the last/first value including its time. The time for @@ -251,18 +353,19 @@ Example: C =item TOTAL Returns the rate from each defined time slot multiplied with the -step size. This can, for instance, return total bytes transfered +step size. This can, for instance, return total bytes transferred when you have logged bytes per second. The time component returns the number of seconds. Example: C -=item PERCENT +=item PERCENT, PERCENTNAN This should follow a B or B I. The I is popped, another number is popped which is a certain percentage (0..100). The data set is then sorted and the value returned is chosen such that I percent of the values is lower or equal than the result. +For PERCENTNAN I values are ignored, but for PERCENT I values are considered lower than any finite number for this purpose so if this operator returns an I you have quite a lot of them in your data. Binite numbers are lesser, or more, than the @@ -270,6 +373,7 @@ finite numbers and are always more than the I numbers. (NaN E -INF E finite values E INF) Example: C + C =item LSLSLOPE, LSLINT, LSLCORREL @@ -296,6 +400,7 @@ Make sure to read L for tipsEtricks. =head1 AUTHOR -Program by Tobias Oetiker Eoetiker@ee.ethz.chE +Program by Tobias Oetiker Etobi@oetiker.chE -This manual page by Alex van den Bogaerdt Ealex@ergens.op.het.netE +This manual page by Alex van den Bogaerdt Ealex@vandenbogaerdt.nlE +with corrections and/or additions by several people