@@ -76,103 +84,90 @@ further down. There is also a number of language bindings for RRDtool which allow you to use it directly from Perl, python, Tcl, PHP, etc.
Set up a new Round Robin Database (RRD). Check the rrdcreate manpage.
Store new data values into an RRD. Check the rrdupdate manpage.
Operationally equivalent to update except for output. Check the rrdupdate manpage.
Create a graph from data stored in one or several RRDs. Apart from +generating graphs, data can also be extracted to stdout. Check the rrdgraph manpage.
Dump the contents of an RRD in plain ASCII. In connection with restore you can use this to move an RRD from one computer architecture to -another. Check the rrddump manpage. +another. Check the rrddump manpage.
Restore an RRD in XML format to a binary RRD. Check the rrdrestore manpage
Get data for a certain time period from a RRD. The graph function +uses fetch to retrieve its data from an RRD. Check the rrdfetch manpage.
Alter setup of an RRD. Check the rrdtune manpage.
Find the last update time of an RRD. Check the rrdlast manpage.
Get information about an RRD. Check the rrdinfo manpage.
Change the size of individual RRAs. This is dangerous! Check the rrdresize manpage.
Export data retrieved from one or several RRDs. Check the rrdxport manpage.
Flush the values for a specific RRD file from memory. Check the rrdflushcached manpage.
This is a standalone tool for producing RRD graphs on the fly. Check +the rrdcgi manpage.
When monitoring the state of a system, it is convenient to have the data available at a constant time interval. Unfortunately, you may not always be able to fetch data at exactly the time you want to. Therefore RRDtool lets you update the logfile at any time you @@ -180,13 +175,12 @@ want. It will automatically interpolate the value of the data-source (DS) at the latest official time-slot (interval) and write this interpolated value to the log. The original value you have supplied is stored as well and is also taken into account when interpolating the -next log entry. +next log entry.
You may log data at a 1 minute interval, but you might also be interested to know the development of the data over the last year. You could do this by simply storing the data in 1 minute intervals for the whole year. While this would take considerable disk space it would @@ -198,18 +192,15 @@ consolidation should occur, and what consolidation function (CF (average, minimum, maximum, total, last) should be used to build the consolidated values (see rrdcreate). You can define any number of different consolidation setups within one RRD. They will all be -maintained on the fly when new data is loaded into the RRD. +maintained on the fly when new data is loaded into the RRD.
Data values of the same consolidation setup are stored into Round Robin Archives (RRA). This is a very efficient manner to store data for a certain amount of time, while using a known and constant amount -of storage space. -
It works like this: If you want to store 1'000 values in 5 minute interval, RRDtool will allocate space for 1'000 data values and a header area. In the header it will store a pointer telling which slots @@ -220,25 +211,20 @@ manner. This automatically limits the history to the last 1'000 values single RRD, you can setup another one, for storing 750 data values at a 2 hour interval, for example, and thus keep a log for the last two months at a lower resolution.
-The use of RRAs guarantees that the RRD does not grow over time and that old data is automatically eliminated. By using the consolidation feature, you can still keep data for a very long time, while gradually reducing the resolution of the data along the time axis.
-Using different consolidation functions (CF) allows you to store exactly the type of information that actually interests you: the maximum one minute traffic on the LAN, the minimum temperature of your wine cellar, the total minutes of down time, etc.
As mentioned earlier, the RRD stores data at a constant interval. Sometimes it may happen that no new data is available when a value has to be written to the RRD. Data acquisition may not be possible for one reason or other. With RRDtool you can handle these @@ -249,40 +235,36 @@ values is accounted for and when a new consolidated value is ready to be written to its Round Robin Archive (RRA), a validity check is performed to make sure that the percentage of unknown values in the data point is above a configurable level. If not, an *UNKNOWN* value -will be written to the RRA. +will be written to the RRA.
RRDtool allows you to generate reports in numerical and graphical form based on the data stored in one or several RRDs. The graphing feature is fully configurable. Size, color and contents of the graph can be defined freely. Check the rrdgraph manpage -for more information on this. -
by Jake Brutlag
RRDtool provides the building blocks for near real-time aberrant behavior detection. These components include:
-An algorithm for predicting the value of a time series one time step +into the future.
+A measure of deviation between predicted and observed values.
+A mechanism to decide if and when an observed value or sequence of +observed values is too deviant from the predicted value(s).
+Here is a brief explanation of these components:
The Holt-Winters time series forecasting algorithm is an on-line (or incremental) algorithm that adaptively predicts future observations in @@ -291,7 +273,7 @@ a time series. Its forecast is the sum of three components: a baseline coefficient (a periodic effect, such as a daily cycle). There is one seasonal coefficient for each time point in the period (cycle). After a value is observed, each of these components is updated via -exponential smoothing. This means that the algorithm ``learns'' from +exponential smoothing. This means that the algorithm "learns" from past values and uses them to predict the future. The rate of adaptation is governed by 3 parameters, alpha (intercept), beta (slope), and gamma (seasonal). The prediction can also be viewed as a @@ -316,6 +298,7 @@ particular, a FAILURES RRA logs potential failures. With these you could, for example, use a front-end application to RRDtool to initiate real-time alerts.
For a detailed description on how to set this up, see the rrdcreate manpage.
+