X-Git-Url: https://git.octo.it/?a=blobdiff_plain;ds=sidebyside;f=doc%2Frrdcreate.pod;h=b321de6329bd8509d373196c92c0a28f07853dbc;hb=06d2116bfef88c41e3a64ca596acdba6ff078c23;hp=8be05671cc3370901e7dd1533b6988bffe44c75d;hpb=5837606887a6d81e8b1f7588525cb1c8783fb62b;p=rrdtool.git
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=head1 NAME
-rrdtool create - Set up a new Round Robin Database
-
-=for html
+rrdcreate - Set up a new Round Robin Database
=head1 SYNOPSIS
-B B I
-S<[B<--start>|B<-b> I]>
-S<[B<--step>|B<-s> I]>
-S<[BIB<:>IB<:>IB<:>IB<:>I]>
-S<[BIB<:>IB<:>IB<:>I]>
+B B I
+S<[B<--start>|B<-b> I]>
+S<[B<--step>|B<-s> I]>
+S<[B<--no-overwrite>]>
+S<[BIB<:>IB<:>I]>
+S<[BIB<:>I]>
=head1 DESCRIPTION
-The create function of the RRDtool lets you set up new
-Round Robin Database (B) files.
-The file is created at its final, full size and filled
-with I<*UNKNOWN*> data.
-
-=over 8
+The create function of RRDtool lets you set up new Round Robin
+Database (B) files. The file is created at its final, full size
+and filled with I<*UNKNOWN*> data.
-=item I
+=head2 I
The name of the B you want to create. B files should end
-with the extension F<.rrd>. However, B will accept any
+with the extension F<.rrd>. However, B will accept any
filename.
-=item B<--start>|B<-b> I (default: now - 10s)
+=head2 B<--start>|B<-b> I (default: now - 10s)
Specifies the time in seconds since 1970-01-01 UTC when the first
-value should be added to the B. B will not accept
+value should be added to the B. B will not accept
any data timed before or at the time specified.
See also AT-STYLE TIME SPECIFICATION section in the
-I documentation for more ways to specify time.
+I documentation for other ways to specify time.
-=item B<--step>|B<-s> I (default: 300 seconds)
+=head2 B<--step>|B<-s> I (default: 300 seconds)
Specifies the base interval in seconds with which data will be fed
into the B.
-=item BIB<:>IB<:>IB<:>IB<:>I
+=head2 B<--no-overwrite>
+
+Do not clobber an existing file of the same name.
-A single B can accept input from several data sources (B).
-(e.g. Incoming and Outgoing traffic on a specific communication
-line). With the B configuration option you must define some basic
-properties of each data source you want to use to feed the B.
+=head2 BIB<:>IB<:>I
+
+A single B can accept input from several data sources (B),
+for example incoming and outgoing traffic on a specific communication
+line. With the B configuration option you must define some basic
+properties of each data source you want to store in the B.
I is the name you will use to reference this particular data
source from an B. A I must be 1 to 19 characters long in
the characters [a-zA-Z0-9_].
-I 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 defines the Data Source Type. The remaining arguments of a
+data source entry depend on the data source type. For GAUGE, COUNTER,
+DERIVE, and ABSOLUTE the format for a data source entry is:
+
+BIB<:>IB<:>IB<:>IB<:>I
-=over 4
+For COMPUTE data sources, the format is:
+
+BIB<:>IB<:>I
+
+In order to decide which data source type to use, review the
+definitions that follow. Also consult the section on "HOW TO MEASURE"
+for further insight.
+
+=over
-=item B
+=item B
-is for things like temperatures or number of people in a
-room or value of a RedHat share.
+is for things like temperatures or number of people in a room or the
+value of a RedHat share.
=item B
-is for continuous incrementing counters like the
-InOctets counter in a router. The B data source assumes that
-the counter never decreases, except when a counter overflows. The update
-function takes the overflow into account. The counter is stored as a
-per-second rate. When the counter overflows, RRDtool checks if the overflow happened at
-the 32bit or 64bit border and acts accordingly by adding an appropriate value to the result.
+is for continuous incrementing counters like the ifInOctets counter in
+a router. The B data source assumes that the counter never
+decreases, except when a counter overflows. The update function takes
+the overflow into account. The counter is stored as a per-second
+rate. When the counter overflows, RRDtool checks if the overflow
+happened at the 32bit or 64bit border and acts accordingly by adding
+an appropriate value to the result.
=item B
will store the derivative of the line going from the last to the
current value of the data source. This can be useful for gauges, for
example, to measure the rate of people entering or leaving a
-room. Internally, derive works exaclty like COUNTER but without
+room. Internally, derive works exactly like COUNTER but without
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.
-=item B
+B
+
+by Don Baarda Edon.baarda@baesystems.comE
+
+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.
+
+=item B
is for counters which get reset upon reading. This is used for fast counters
which tend to overflow. So instead of reading them normally you reset them
-after every read to make sure you have a maximal time available before the
+after every read to make sure you have a maximum time available before the
next overflow. Another usage is for things you count like number of messages
since the last update.
+=item B
+
+is for storing the result of a formula applied to other data sources
+in the B. 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, such data sets are referred
+to as "virtual" or "computed" columns.
+
=back
I defines the maximum number of seconds that may pass
-between two updates of this data source before the value of the
+between two updates of this data source before the value of the
data source is assumed to be I<*UNKNOWN*>.
-I and I are optional entries defining the expected range of
-the data supplied by this data source. If I and/or I are
-defined, any value outside the defined range will be regarded as
-I<*UNKNOWN*>. If you do not know or care about min and max, set them
-to U for unknown. Note that min and max always refer to the processed values
-of the DS. For a traffic-B type DS this would be the max and min
-data-rate expected from the device.
+I and I define the expected range values for data supplied by a
+data source. If I and/or I any value outside the defined range
+will be regarded as I<*UNKNOWN*>. If you do not know or care about min and
+max, set them to U for unknown. Note that min and max always refer to the
+processed values of the DS. For a traffic-B type DS this would be
+the maximum and minimum data-rate expected from the device.
I
-=item BIB<:>IB<:>IB<:>I
+I defines the formula used to compute the PDPs of a
+COMPUTE data source from other data sources in the same . It is
+similar to defining a B 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: COUNT, 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 Bs must refer only to Bs
+and Bs previously defined in the same graph command.
+
+=head2 BIB<:>I
The purpose of an B is to store data in the round robin archives
-(B). An archive consists of a number of data values from all the
-defined data-sources (B) and is defined with an B line.
+(B). An archive consists of a number of data values or statistics for
+each of the defined data-sources (B) and is defined with an B line.
+
+When data is entered into an B, it is first fit into time slots
+of the length defined with the B<-s> option, thus becoming a I.
-When data is entered into an B, it is first fit into time slots of
-the length defined with the B<-s> option becoming a I.
+The data is also processed with the consolidation function (I) of
+the archive. There are several consolidation functions that
+consolidate primary data points via an aggregate function: B,
+B, B, B.
-The data is also consolidated with the consolidation function (I)
-of the archive. The following consolidation functions are defined:
-B, B, B, B.
+=over
+
+=item AVERAGE
+
+the average of the data points is stored.
+
+=item MIN
+
+the smallest of the data points is stored.
+
+=item MAX
+
+the largest of the data points is stored.
+
+=item LAST
+
+the last data points is used.
+
+=back
+
+Note that data aggregation inevitably leads to loss of precision and
+information. The trick is to pick the aggregate function such that the
+I properties of your data is kept across the aggregation
+process.
+
+
+The format of B line for these
+consolidation functions is:
+
+BIB<:>IB<:>IB<:>I
I 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.
+regarded as known. It is given as the ratio of allowed I<*UNKNOWN*> PDPs
+to the number of PDPs in the interval. Thus, it ranges from 0 to 1 (exclusive).
-I defines how many of these I are used to
-build a I which then goes into the archive.
+
+I defines how many of these I are used to build
+a I which then goes into the archive.
I defines how many generations of data values are kept in an B.
+Obviously, this has to be greater than zero.
+
+=head1 Aberrant Behavior Detection with Holt-Winters Forecasting
+
+In addition to the aggregate functions, there are a set of specialized
+functions that enable B to provide data smoothing (via the
+Holt-Winters forecasting algorithm), confidence bands, and the
+flagging aberrant behavior in the data source time series:
+
+=over
+
+=item *
+
+BIB<:>IB<:>IB<:>IB<:>I[B<:>I]
+
+=item *
+
+BIB<:>IB<:>IB<:>IB<:>I[B<:>I]
+
+=item *
+
+BIB<:>IB<:>IB<:>I[B<:smoothing-window=>I]
+
+=item *
+
+BIB<:>IB<:>IB<:>I[B<:smoothing-window=>I]
+
+=item *
+
+BIB<:>IB<:>I
+
+=item *
+
+BIB<:>IB<:>IB<:>IB<:>I
+
+=back
+
+These B differ from the true consolidation functions in several ways.
+First, each of the Bs is updated once for every primary data point.
+Second, these B are interdependent. To generate real-time confidence
+bounds, a matched set of SEASONAL, DEVSEASONAL, DEVPREDICT, and either
+HWPREDICT or MHWPREDICT must exist. Generating smoothed values of the primary
+data points requires a SEASONAL B and either an HWPREDICT or MHWPREDICT
+B. Aberrant behavior detection requires FAILURES, DEVSEASONAL, SEASONAL,
+and either HWPREDICT or MHWPREDICT.
+
+The predicted, or smoothed, values are stored in the HWPREDICT or MHWPREDICT
+B. HWPREDICT and MHWPREDICT are actually two variations on the
+Holt-Winters method. They are interchangeable. Both attempt to decompose data
+into three components: a baseline, a trend, and a seasonal coefficient.
+HWPREDICT adds its seasonal coefficient to the baseline to form a prediction, whereas
+MHWPREDICT multiplies its seasonal coefficient by the baseline to form a
+prediction. The difference is noticeable when the baseline changes
+significantly in the course of a season; HWPREDICT will predict the seasonality
+to stay constant as the baseline changes, but MHWPREDICT will predict the
+seasonality to grow or shrink in proportion to the baseline. The proper choice
+of method depends on the thing being modeled. For simplicity, the rest of this
+discussion will refer to HWPREDICT, but MHWPREDICT may be substituted in its
+place.
+
+The predicted deviations are stored in DEVPREDICT (think a standard deviation
+which can be scaled to yield a confidence band). The FAILURES B stores
+binary indicators. A 1 marks the indexed observation as 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 to graph
+confidence bounds and failures appears in L.
+
+The SEASONAL and DEVSEASONAL B 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 will have 288 rows.
+
+In order to simplify the creation for the novice user, in addition to
+supporting explicit creation of the HWPREDICT, SEASONAL, DEVPREDICT,
+DEVSEASONAL, and FAILURES B, the B create command supports
+implicit creation of the other four when HWPREDICT is specified alone and
+the final argument I is omitted.
+
+I specifies the length of the B 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 should be larger than
+the I. If the DEVPREDICT B is implicitly created, the
+default number of rows is the same as the HWPREDICT I argument. If the
+FAILURES B is implicitly created, I will be set to the I argument of the HWPREDICT B. Of course, the B
+I command is available if these defaults are not sufficient and the
+creator wishes to avoid explicit creations of the other specialized function
+B.
+
+I specifies the number of primary data points in a seasonal
+cycle. If SEASONAL and DEVSEASONAL are implicitly created, this argument for
+those B is set automatically to the value specified by HWPREDICT. If
+they are explicitly created, the creator should verify that all three
+I arguments agree.
+
+I is the adaption parameter of the intercept (or baseline)
+coefficient in the Holt-Winters forecasting algorithm. See L for a
+description of this algorithm. I 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 means
+that past history carries greater weight in predicting the baseline
+component.
+
+I is the adaption parameter of the slope (or linear trend) coefficient
+in the Holt-Winters forecasting algorithm. I must lie between 0 and 1
+and plays the same role as I with respect to the predicted linear
+trend.
+
+I 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 are created
+implicitly, they will both have the same value for I: the value
+specified for the HWPREDICT I argument. Note that because there is
+one seasonal coefficient (or deviation) for each time point during the
+seasonal cycle, the adaptation 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 are created explicitly, I need not
+be the same for both. Note that I can also be changed via the
+B I command.
+
+I specifies the fraction of a season that should be
+averaged around each point. By default, the value of I is
+0.05, which means each value in SEASONAL and DEVSEASONAL will be occasionally
+replaced by averaging it with its (I*0.05) nearest neighbors.
+Setting I to zero will disable the running-average smoother
+altogether.
+
+I provides the links between related B. If HWPREDICT is
+specified alone and the other B are created implicitly, then
+there is no need to worry about this argument. If B are created
+explicitly, then carefully pay attention to this argument. For each
+B which includes this argument, there is a dependency between
+that B and another B. The I argument is the 1-based
+index in the order of B creation (that is, the order they appear
+in the I command). The dependent B for each B
+requiring the I