@@ -51,7 +59,7 @@ data point on the graph. VDEF instructions work on an entire da one run. Note, that currently VDEF instructions only support a limited list of functions.
Example: VDEF:maximum=mydata,MAXIMUM
This will set variable ``maximum'' which you now can use in the rest +
This will set variable "maximum" which you now can use in the rest of your RRD script.
Example: CDEF:mydatabits=mydata,8,*
This means: push variable mydata, push the number 8, execute
@@ -69,173 +77,92 @@ would do a = b, 3, +, 5, * without the need for parentheses.
LT, LE, GT, GE, EQ, NE
Pop two elements from the stack, compare them for the selected condition and return 1 for true or 0 for false. Comparing an unknown or an infinite value will always result in 0 (false).
-UN, ISINF
-Pop one element from the stack, compare this to unknown respectively to positive or negative infinity. Returns 1 for true or 0 for false.
-IF
-Pops three elements from the stack. If the element popped last is 0 (false), the value popped first is pushed back onto the stack, otherwise the value popped second is pushed back. This does, indeed, mean that any value other than 0 is considered to be true.
-Example: A,B,C,IF should be read as if (A) then (B) else (C)
MIN, MAX
Pops two elements from the stack and returns the smaller or larger, respectively. Note that infinite is larger than anything else. If one of the input numbers is unknown then the result of the operation will be unknown too.
-LIMIT
-Pops two elements from the stack and uses them to define a range. Then it pops another element and if it falls inside the range, it is pushed back. If not, an unknown is pushed.
-The range defined includes the two boundaries (so: a number equal to one of the boundaries will be pushed back). If any of the three numbers involved is either unknown or infinite this function will always return an unknown
-Example: CDEF:a=alpha,0,100,LIMIT will return unknown if
alpha is lower than 0 or if it is higher than 100.
+, -, *, /, %
Add, subtract, multiply, divide, modulo
-ADDNAN
-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.
-SIN, COS, LOG, EXP, SQRT
-Sine and cosine (input in radians), log and exp (natural logarithm), square root.
-ATAN
-Arctangent (output in radians).
-ATAN2
-Arctangent of y,x components (output in radians). This pops one element from the stack, the x (cosine) component, and then a second, which is the y (sine) component. It then pushes the arctangent of their ratio, resolving the ambiguity between quadrants.
-Example: CDEF:angle=Y,X,ATAN2,RAD2DEG will convert X,Y
components into an angle in degrees.
FLOOR, CEIL
-Round down or up to the nearest integer.
-DEG2RAD, RAD2DEG
-Convert angle in degrees to radians, or radians to degrees.
-ABS
-Take the absolute value.
SORT, REV
Pop one element from the stack. This is the count of items to be sorted (or reversed). The top count of the remaining elements are then sorted (or reversed) in place on the stack.
-Example: CDEF:x=v1,v2,v3,v4,v5,v6,6,SORT,POP,5,REV,POP,+,+,+,4,/ will
compute the average of the values v1 to v6 after removing the smallest and
largest.
AVG
-Pop one element (count) from the stack. Now pop count elements and build the average, ignoring all UNKNOWN values in the process.
-Example: CDEF:x=a,b,c,d,4,AVG
TREND, TRENDNAN
-Create a ``sliding window'' average of another data series.
-Create a "sliding window" average of another data series.
Usage: CDEF:smoothed=x,1800,TREND
-This will create a half-hour (1800 second) sliding window average of x. The average is essentially computed as shown here:
-
+---!---!---!---!---!---!---!---!--->
now
@@ -245,45 +172,27 @@ average is essentially computed as shown here:
<--------------->
delay t2
<--------------->
-
Value at sample (t0) will be the average between (t0-delay) and (t0)
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.
-PREDICT, PREDICTSIGMA
-Create a ``sliding window'' average/sigma of another data series, that also +
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=<shift n>,...,<shift 1>,n,<window>,x,PREDICT CDEF:sigma=<shift n>,...,<shift 1>,n,<window>,x,PREDICTSIGMA
-Usage - shifts defined as a base shift and a number of time this is applied CDEF:predict=<shift multiplier>,-n,<window>,x,PREDICT CDEF:sigma=<shift multiplier>,-n,<window>,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
@@ -303,26 +212,18 @@ average is essentially computed as shown here:
<----------------------------------------------->
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 \ @@ -336,153 +237,100 @@ This also shows if the prediction is exceeded at a certain point.
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 behaviour. 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-
UNKN
Pushes an unknown value on the stack
-INF, NEGINF
-Pushes a positive or negative infinite value on the stack. When such a value is graphed, it appears at the top or bottom of the graph, no matter what the actual value on the y-axis is.
-PREV
-Pushes an unknown value if this is the first value of a data set or otherwise the result of this CDEF at the previous time step. This allows you to do calculations across the data. This function cannot be used in VDEF instructions.
-PREV(vname)
-Pushes an unknown value if this is the first value of a data set or otherwise the result of the vname variable at the previous time step. This allows you to do calculations across the data. This function cannot be used in VDEF instructions.
-COUNT
-Pushes the number 1 if this is the first value of the data set, the number 2 if it is the second, and so on. This special value allows you to make calculations based on the position of the value within the data set. This function cannot be used in VDEF instructions.
Thu Jan 1 00:00:00 UTC 1970.
-Time inside RRDtool is measured in seconds since the epoch. The
+epoch is defined to be Thu Jan 1 00:00:00 UTC 1970.
NOW
-Pushes the current time on the stack.
-TIME
-Pushes the time the currently processed value was taken at onto the stack.
-LTIME
-Takes the time as defined by TIME, applies the time zone offset valid at that time including daylight saving time if your OS supports it, and pushes the result on the stack. There is an elaborate example in the examples section below on how to use this.
DUP, POP, EXC
Duplicate the top element, remove the top element, exchange the two top elements.
-
These operators work only on VDEF statements. Note that currently ONLY these work for VDEF.
Return the corresponding value, MAXIMUM and MINIMUM also return +the first occurrence of that value in the time component.
Example: VDEF:avg=mydata,AVERAGE
Returns the standard deviation of the values.
Example: VDEF:stdev=mydata,STDEV
Return the last/first value including its time. The time for FIRST is actually the start of the corresponding interval, whereas -LAST returns the end of the corresponding interval. -
Example: VDEF:first=mydata,FIRST
Returns the rate from each defined time slot multiplied with the step size. This can, for instance, return total bytes transfered when you have logged bytes per second. The time component returns -the number of seconds. -
Example: VDEF:total=mydata,TOTAL
This should follow a DEF or CDEF vname. The vname 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 percentage percent of the values is lower or equal than the result. @@ -491,28 +339,23 @@ For PERCENTNAN Unknown values are ignored, but for PERCENT purpose so if this operator returns an unknown you have quite a lot of them in your data. Infinite numbers are lesser, or more, than the finite numbers and are always more than the Unknown numbers. -(NaN < -INF < finite values < INF) -
Example: VDEF:perc95=mydata,95,PERCENT
VDEF:percnan95=mydata,95,PERCENTNAN
Return the parameters for a Least Squares Line (y = mx +b) which approximate the provided dataset. LSLSLOPE is the slope (m) of the line related to the COUNT position of the data. LSLINT is the y-intercept (b), which happens also to be the first data point on the graph. LSLCORREL is the Correlation Coefficient (also know as Pearson's Product Moment Correlation Coefficient). It will range from 0 to +/-1 -and represents the quality of fit for the approximation. -
Example: VDEF:slope=mydata,LSLSLOPE