B<rrdtool> B<create> I<filename>
S<[B<--start>|B<-b> I<start time>]>
S<[B<--step>|B<-s> I<step>]>
-S<[B<DS:>I<ds-name>B<:>I<DST>B<:>I<heartbeat>B<:>I<min>B<:>I<max>]>
-S<[B<RRA:>I<CF>B<:>I<xff>B<:>I<steps>B<:>I<rows>]>
+S<[B<DS:>I<ds-name>B<:>I<DST>B<:>I<dst arguments>]>
+I<heartbeat>B<:>I<min>B<:>I<max>]>
+S<[B<RRA:>I<CF>B<:>I<cf arguments>]>
=head1 DESCRIPTION
Specifies the base interval in seconds with which data will be fed
into the B<RRD>.
-=item B<DS:>I<ds-name>B<:>I<DST>B<:>I<heartbeat>B<:>I<min>B<:>I<max>
+=item B<DS:>I<ds-name>B<:>I<DST>B<:>I<dst arguments>
A single B<RRD> can accept input from several data sources (B<DS>).
(e.g. Incoming and Outgoing traffic on a specific communication
source from an B<RRD>. A I<ds-name> must be 1 to 19 characters long in
the characters [a-zA-Z0-9_].
-I<DST> defines the Data Source Type. See the section on "How to Measure" below for further insight.
-The Datasource Type must be onw of the following:
+I<DST> defines the Data Source Type. The remaining arguments of a
+data source entry depend upon the data source type. For GAUGE, COUNTER,
+DERIVE, and ABSOLUTE the format for a data source entry is:
+
+B<DS:>I<ds-name>B<:>I<GAUGE | COUNTER | DERIVE | ABSOLUTE>B<:>I<heartbeat>B<:>I<min>B<:>I<max>
+
+For COMPUTE data sources, the format is:
+
+B<DS:>I<ds-name>B<:>I<COMPUTE>B<:>I<rpn-expression>
+
+To decide on a data source type, review the definitions that follow.
+Consult the section on "HOW TO MEASURE" for further insight.
=over 4
overflow checks. So if your counter does not reset at 32 or 64 bit you
might want to use DERIVE and combine it with a MIN value of 0.
+=over
+
+=item NOTE on COUNTER vs DERIVE
+
+by Don Baarda E<lt>don.baarda@baesystems.comE<gt>
+
+If you cannot tolerate ever mistaking the occasional counter reset for a
+legitimate counter wrap, and would prefer "Unknowns" for all legitimate
+counter wraps and resets, always use DERIVE with min=0. Otherwise, using
+COUNTER with a suitable max will return correct values for all legitimate
+counter wraps, mark some counter resets as "Unknown", but can mistake some
+counter resets for a legitimate counter wrap.
+
+For a 5 minute step and 32-bit counter, the probability of mistaking a
+counter reset for a legitimate wrap is arguably about 0.8% per 1Mbps of
+maximum bandwidth. Note that this equates to 80% for 100Mbps interfaces, so
+for high bandwidth interfaces and a 32bit counter, DERIVE with min=0 is
+probably preferable. If you are using a 64bit counter, just about any max
+setting will eliminate the possibility of mistaking a reset for a counter
+wrap.
+
+=back
+
=item B<ABSOLUTE>
is for counters which get reset upon reading. This is used for fast counters
next overflow. Another usage is for things you count like number of messages
since the last update.
+=item B<COMPUTE>
+
+is for storing the result of a formula applied to other data sources in
+the B<RRD>. This data source is not supplied a value on update, but rather
+its Primary Data Points (PDPs) are computed from the PDPs of the data sources
+according to the rpn-expression that defines the formula. Consolidation
+functions are then applied normally to the PDPs of the COMPUTE data source
+(that is the rpn-expression is only applied to generate PDPs). In database
+software, these are referred to as "virtual" or "computed" columns.
+
=back
I<heartbeat> defines the maximum number of seconds that may pass
always set the min and/or max properties. This will help RRDtool in
doing a simple sanity check on the data supplied when running update.>
-=item B<RRA:>I<CF>B<:>I<xff>B<:>I<steps>B<:>I<rows>
+I<rpn-expression> defines the formula used to compute the PDPs of a COMPUTE
+data source from other data sources in the same <RRD>. It is similar to defining
+a B<CDEF> argument for the graph command. Please refer to that manual page
+for a list and description of RPN operations supported. For
+COMPUTE data sources, the following RPN operations are not supported: PREV,
+TIME, and LTIME. In addition, in defining the RPN expression, the COMPUTE
+data source may only refer to the names of data source listed previously
+in the create command. This is similar to the restriction that B<CDEF>s must
+refer only to B<DEF>s and B<CDEF>s previously defined in the same graph command.
+
+=item B<RRA:>I<CF>B<:>I<cf arguments>
+
The purpose of an B<RRD> is to store data in the round robin archives
-(B<RRA>). An archive consists of a number of data values from all the
-defined data-sources (B<DS>) and is defined with an B<RRA> line.
+(B<RRA>). An archive consists of a number of data values or statistics for
+each of the defined data-sources (B<DS>) and is defined with an B<RRA> line.
When data is entered into an B<RRD>, it is first fit into time slots of
the length defined with the B<-s> option becoming a I<primary data point>.
-The data is also consolidated with the consolidation function (I<CF>)
-of the archive. The following consolidation functions are defined:
-B<AVERAGE>, B<MIN>, B<MAX>, B<LAST>.
+The data is also processed with the consolidation function (I<CF>)
+of the archive. There are several consolidation functions that consolidate
+primary data points via an aggregate function: B<AVERAGE>, B<MIN>, B<MAX>, B<LAST>.
+The format of B<RRA> line for these consolidation functions is:
+
+B<RRA:>I<AVERAGE | MIN | MAX | LAST>B<:>I<xff>B<:>I<steps>B<:>I<rows>
I<xff> The xfiles factor defines what part of a consolidation interval may
be made up from I<*UNKNOWN*> data while the consolidated value is still
regarded as known.
-I<steps> defines how many of these I<primary data points> are used to
-build a I<consolidated data point> which then goes into the archive.
+I<steps> defines how many of these I<primary data points> are used to build
+a I<consolidated data point> which then goes into the archive.
I<rows> defines how many generations of data values are kept in an B<RRA>.
=back
+=head1 Aberrant Behavior Detection with Holt-Winters Forecasting
+
+by Jake Brutlag E<lt>jakeb@corp.webtv.netE<gt>
+
+In addition to the aggregate functions, there are a set of specialized
+functions that enable B<RRDtool> to provide data smoothing (via the
+Holt-Winters forecasting algorithm), confidence bands, and the flagging
+aberrant behavior in the data source time series:
+
+=over 4
+
+=item B<RRA:>I<HWPREDICT>B<:>I<rows>B<:>I<alpha>B<:>I<beta>B<:>I<seasonal period>B<:>I<rra num>
+
+=item B<RRA:>I<SEASONAL>B<:>I<seasonal period>B<:>I<gamma>B<:>I<rra num>
+
+=item B<RRA:>I<DEVSEASONAL>B<:>I<seasonal period>B<:>I<gamma>B<:>I<rra num>
+
+=item B<RRA:>I<DEVPREDICT>B<:>I<rows>B<:>I<rra num>
+
+=item B<RRA:>I<FAILURES>B<:>I<rows>B<:>I<threshold>B<:>I<window length>B<:>I<rra num>
+
+=back
+
+These B<RRAs> differ from the true consolidation functions in several ways.
+First, each of the B<RRA>s is updated once for every primary data point.
+Second, these B<RRAs> are interdependent. To generate real-time confidence
+bounds, then a matched set of HWPREDICT, SEASONAL, DEVSEASONAL, and
+DEVPREDICT must exist. Generating smoothed values of the primary data points
+requires both a HWPREDICT B<RRA> and SEASONAL B<RRA>. Aberrant behavior
+detection requires FAILURES, HWPREDICT, DEVSEASONAL, and SEASONAL.
+
+The actual predicted, or smoothed, values are stored in the HWPREDICT
+B<RRA>. The predicted deviations are store in DEVPREDICT (think a standard
+deviation which can be scaled to yield a confidence band). The FAILURES
+B<RRA> stores binary indicators. A 1 marks the indexed observation a
+failure; that is, the number of confidence bounds violations in the
+preceding window of observations met or exceeded a specified threshold. An
+example of using these B<RRAs> to graph confidence bounds and failures
+appears in L<rrdgraph>.
+
+The SEASONAL and DEVSEASONAL B<RRAs> store the seasonal coefficients for the
+Holt-Winters Forecasting algorithm and the seasonal deviations respectively.
+There is one entry per observation time point in the seasonal cycle. For
+example, if primary data points are generated every five minutes, and the
+seasonal cycle is 1 day, both SEASONAL and DEVSEASONAL with have 288 rows.
+
+In order to simplify the creation for the novice user, in addition to
+supporting explicit creation the HWPREDICT, SEASONAL, DEVPREDICT,
+DEVSEASONAL, and FAILURES B<RRAs>, the B<rrdtool> create command supports
+implicit creation of the other four when HWPREDICT is specified alone and
+the final argument I<rra num> is omitted.
+
+I<rows> specifies the length of the B<RRA> prior to wrap around. Remember
+that there is a one-to-one correspondence between primary data points and
+entries in these RRAs. For the HWPREDICT CF, I<rows> should be larger than
+the I<seasonal period>. If the DEVPREDICT B<RRA> is implicity created, the
+default number of rows is the same as the HWPREDICT I<rows> argument. If the
+FAILURES B<RRA> is implicitly created, I<rows> will be set to the I<seasonal
+period> argument of the HWPREDICT B<RRA>. Of course, the B<rrdtool>
+I<resize> command is available if these defaults are not sufficient and the
+create wishes to avoid explicit creations of the other specialized function
+B<RRAs>.
+
+I<seasonal period> specifies the number of primary data points in a seasonal
+cycle. If SEASONAL and DEVSEASONAL are implicitly created, this argument for
+those B<RRAs> is set automatically to the value specified by HWPREDICT. If
+they are explicity created, the creator should verify that all three
+I<seasonal period> arguments agree.
+
+I<alpha> is the adaptation parameter of the intercept (or baseline)
+coefficient in the Holt-Winters Forecasting algorithm. See L<rrdtool> for a
+description of this algorithm. I<alpha> must lie between 0 and 1. A value
+closer to 1 means that more recent observations carry greater weight in
+predicting the baseline component of the forecast. A value closer to 0 mean
+that past history carries greater weight in predicted the baseline
+component.
+
+I<beta> is the adaption parameter of the slope (or linear trend) coefficient
+in the Holt-Winters Forecating algorihtm. I<beta> must lie between 0 and 1
+and plays the same role as I<alpha> with respect to the predicted linear
+trend.
+
+I<gamma> is the adaption parameter of the seasonal coefficients in the
+Holt-Winters Forecasting algorithm (HWPREDICT) or the adaption parameter in
+the exponential smoothing update of the seasonal deviations. It must lie
+between 0 and 1. If the SEASONAL and DEVSEASONAL B<RRAs> are created
+implicitly, they will both have the same value for I<gamma>: the value
+specified for the HWPREDICT I<alpha> argument. Note that because there is
+one seasonal coefficient (or deviation) for each time point during the
+seasonal cycle, the adaption rate is much slower than the baseline. Each
+seasonal coefficient is only updated (or adapts) when the observed value
+occurs at the offset in the seasonal cycle corresponding to that
+coefficient.
+
+If SEASONAL and DEVSEASONAL B<RRAs> are created explicity, I<gamma> need not
+be the same for both. Note that I<gamma> can also be changed via the
+B<rrdtool> I<tune> command.
+
+I<rra num> provides the links between related B<RRAs>. If HWPREDICT is
+specified alone and the other B<RRAs> created implicitly, then there is no
+need to worry about this argument. If B<RRAs> are created explicitly, then
+pay careful attention to this argument. For each B<RRA> which includes this
+argument, there is a dependency between that B<RRA> and another B<RRA>. The
+I<rra num> argument is the 1-based index in the order of B<RRA> creation
+(that is, the order they appear in the I<create> command). The dependent
+B<RRA> for each B<RRA> requiring the I<rra num> argument is listed here:
+
+=over 4
+
+=item *
+
+HWPREDICT I<rra num> is the index of the SEASONAL B<RRA>.
+
+=item *
+
+SEASONAL I<rra num> is the index of the HWPREDICT B<RRA>.
+
+=item *
+
+DEVPREDICT I<rra num> is the index of the DEVSEASONAL B<RRA>.
+
+=item *
+
+DEVSEASONAL I<rra num> is the index of the HWPREDICT B<RRA>.
+
+=item *
+
+FAILURES I<rra num> is the index of the DEVSEASONAL B<RRA>.
+
+=back
+
+I<threshold> is the minimum number of violations (observed values outside
+the confidence bounds) within a window that constitutes a failure. If the
+FAILURES B<RRA> is implicitly created, the default value is 7.
+
+I<window length> is the number of time points in the window. Specify an
+integer greater than or equal to the threshold and less than or equal to 28.
+The time interval this window represents depends on the interval between
+primary data points. If the FAILURES B<RRA> is implicity created, the
+default value is 9.
+
=head1 The HEARTBEAT and the STEP
Here is an explanation by Don Baarda on the inner workings of rrdtool.
third and the fourth RRA's do the same with the for the maximum and
average temperature, respectively.
+=head1 EXAMPLE 2
+
+C<rrdtool create monitor.rrd --step 300
+DS:ifOutOctets:COUNTER:1800:0:4294967295
+RRA:AVERAGE:0.5:1:2016
+RRA:HWPREDICT:1440:0.1:0.0035:288>
+
+This example is a monitor of a router interface. The first B<RRA> tracks the
+traffic flow in octects; the second B<RRA> generates the specialized
+functions B<RRAs> for aberrant behavior detection. Note that the I<rra num>
+argument of HWPREDICT is missing, so the other B<RRAs> will be implicitly be
+created with default parameter values. In this example, the forecasting
+algorithm baseline adapts quickly; in fact the most recent one hour of
+observations (each at 5 minute intervals) account for 75% of the baseline
+prediction. The linear trend forecast adapts much more slowly. Observations
+made in during the last day (at 288 observations per day) account for only
+65% of the predicted linear trend. Note: these computations rely on an
+exponential smoothing formula described in a forthcoming LISA 2000 paper.
+
+The seasonal cycle is one day (288 data points at 300 second intervals), and
+the seasonal adaption paramter will be set to 0.1. The RRD file will store 5
+days (1440 data points) of forecasts and deviation predictions before wrap
+around. The file will store 1 day (a seasonal cycle) of 0-1 indicators in
+the FAILURES B<RRA>.
+
+The same RRD file and B<RRAs> are created with the following command, which explicitly
+creates all specialized function B<RRAs>.
+
+C<rrdtool create monitor.rrd --step 300
+DS:ifOutOctets:COUNTER:1800:0:4294967295
+RRA:AVERAGE:0.5:1:2016
+RRA:HWPREDICT:1440:0.1:0.0035:288:3
+RRA:SEASONAL:288:0.1:2
+RRA:DEVPREDICT:1440:5
+RRA:DEVSEASONAL:288:0.1:2
+RRA:FAILURES:288:7:9:5>
+
+Of course, explicit creation need not replicate implicit create, a number of arguments
+could be changed.
+
+=head1 EXAMPLE 3
+
+C<rrdtool create proxy.rrd --step 300
+DS:TotalRequests:DERIVE:1800:0:U
+DS:AccumDuration:DERIVE:1800:0:U
+DS:AvgReqDuration:COMPUTE:AccumDuration,TotalRequests,0,EQ,1,TotalRequests,IF,/
+RRA:AVERAGE:0.5:1:2016>
+
+This example is monitoring the average request duration during each 300 sec
+interval for requests processed by a web proxy during the interval.
+In this case, the proxy exposes two counters, the number of requests
+processed since boot and the total cumulative duration of all processed
+requests. Clearly these counters both have some rollover point, but using the
+DERIVE data source also handles the reset that occurs when the web proxy is
+stopped and restarted.
+
+In the B<RRD>, the first data source stores the requests per second rate
+during the interval. The second data source stores the total duration of all
+requests processed during the interval divided by 300. The COMPUTE data source
+divides each PDP of the AccumDuration by the corresponding PDP of
+TotalRequests and stores the average request duration. The remainder of the
+RPN expression handles the divide by zero case.
+
=head1 AUTHOR
Tobias Oetiker E<lt>oetiker@ee.ethz.chE<gt>
projects / rrdtool.git / blobdiff