![[tokkee]](http://tokkee.org/images/avatar.png){kind=avatar}
diff --git a/doc/rrdcreate.html b/doc/rrdcreate.html
index 97172f63f487218bfe49fc41ab5cb649fa2ba19a..42f0aa4210b5ca9d214f0031913811772cf58365 100644 (file)
--- a/doc/rrdcreate.html
+++ b/doc/rrdcreate.html
-<?xml version="1.0" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>rrdcreate</title>
-<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<link rev="made" href="mailto:root@localhost" />
</head>
definitions that follow. Also consult the section on ``HOW TO MEASURE''
for further insight.</p>
<dl>
-<dt><strong><a name="item_gauge"><strong>GAUGE</strong></a></strong></dt>
-
+<dt><strong><a name="item_gauge"><strong>GAUGE</strong></a></strong><br />
+</dt>
<dd>
-<p>is for things like temperatures or number of people in a room or the
-value of a RedHat share.</p>
+is for things like temperatures or number of people in a room or the
+value of a RedHat share.
</dd>
-<dt><strong><a name="item_counter"><strong>COUNTER</strong></a></strong></dt>
-
+<p></p>
+<dt><strong><a name="item_counter"><strong>COUNTER</strong></a></strong><br />
+</dt>
<dd>
-<p>is for continuous incrementing counters like the ifInOctets counter in
+is for continuous incrementing counters like the ifInOctets counter in
a router. The <strong>COUNTER</strong> 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.</p>
+an appropriate value to the result.
</dd>
-<dt><strong><a name="item_derive"><strong>DERIVE</strong></a></strong></dt>
-
+<p></p>
+<dt><strong><a name="item_derive"><strong>DERIVE</strong></a></strong><br />
+</dt>
<dd>
-<p>will store the derivative of the line going from the last to the
+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 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.</p>
+might want to use DERIVE and combine it with a MIN value of 0.
+</dd>
+<dd>
<p><strong>NOTE on COUNTER vs DERIVE</strong></p>
+</dd>
+<dd>
<p>by Don Baarda <<a href="mailto:don.baarda@baesystems.com">don.baarda@baesystems.com</a>></p>
+</dd>
+<dd>
<p>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.</p>
+</dd>
+<dd>
<p>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
setting will eliminate the possibility of mistaking a reset for a counter
wrap.</p>
</dd>
-<dt><strong><a name="item_absolute"><strong>ABSOLUTE</strong></a></strong></dt>
-
+<p></p>
+<dt><strong><a name="item_absolute"><strong>ABSOLUTE</strong></a></strong><br />
+</dt>
<dd>
-<p>is for counters which get reset upon reading. This is used for fast counters
+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 maximum time available before the
next overflow. Another usage is for things you count like number of messages
-since the last update.</p>
+since the last update.
</dd>
-<dt><strong><a name="item_compute"><strong>COMPUTE</strong></a></strong></dt>
-
+<p></p>
+<dt><strong><a name="item_compute"><strong>COMPUTE</strong></a></strong><br />
+</dt>
<dd>
-<p>is for storing the result of a formula applied to other data sources
+is for storing the result of a formula applied to other data sources
in the <strong>RRD</strong>. 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.</p>
+to as ``virtual'' or ``computed'' columns.
</dd>
-</dl>
+<p></p></dl>
<p><em>heartbeat</em> defines the maximum number of seconds that may pass
between two updates of this data source before the value of the
data source is assumed to be <em>*UNKNOWN*</em>.</p>
consolidate primary data points via an aggregate function: <strong>AVERAGE</strong>,
<strong>MIN</strong>, <strong>MAX</strong>, <strong>LAST</strong>.</p>
<dl>
-<dt><strong><a name="item_average">AVERAGE</a></strong></dt>
-
+<dt><strong><a name="item_average">AVERAGE</a></strong><br />
+</dt>
<dd>
-<p>the average of the data points is stored.</p>
+the average of the data points is stored.
</dd>
-<dt><strong><a name="item_min">MIN</a></strong></dt>
-
+<p></p>
+<dt><strong><a name="item_min">MIN</a></strong><br />
+</dt>
<dd>
-<p>the smallest of the data points is stored.</p>
+the smallest of the data points is stored.
</dd>
-<dt><strong><a name="item_max">MAX</a></strong></dt>
-
+<p></p>
+<dt><strong><a name="item_max">MAX</a></strong><br />
+</dt>
<dd>
-<p>the largest of the data points is stored.</p>
+the largest of the data points is stored.
</dd>
-<dt><strong><a name="item_last">LAST</a></strong></dt>
-
+<p></p>
+<dt><strong><a name="item_last">LAST</a></strong><br />
+</dt>
<dd>
-<p>the last data points is used.</p>
+the last data points is used.
</dd>
-</dl>
+<p></p></dl>
<p>Note that data aggregation inevitably leads to loss of precision and
information. The trick is to pick the aggregate function such that the
<em>interesting</em> properties of your data is kept across the aggregation
@@ -242,25 +255,24 @@ functions that enable <strong>RRDtool</strong> to provide data smoothing (via th
Holt-Winters forecasting algorithm), confidence bands, and the
flagging aberrant behavior in the data source time series:</p>
<ul>
-<li>
-<p><strong>RRA:</strong><em>HWPREDICT</em><strong>:</strong><em>rows</em><strong>:</strong><em>alpha</em><strong>:</strong><em>beta</em><strong>:</strong><em>seasonal period</em>[<strong>:</strong><em>rra-num</em>]</p>
-</li>
-<li>
-<p><strong>RRA:</strong><em>MHWPREDICT</em><strong>:</strong><em>rows</em><strong>:</strong><em>alpha</em><strong>:</strong><em>beta</em><strong>:</strong><em>seasonal period</em>[<strong>:</strong><em>rra-num</em>]</p>
-</li>
-<li>
-<p><strong>RRA:</strong><em>SEASONAL</em><strong>:</strong><em>seasonal period</em><strong>:</strong><em>gamma</em><strong>:</strong><em>rra-num</em>[<strong>:smoothing-window=</strong><em>fraction</em>]</p>
-</li>
-<li>
-<p><strong>RRA:</strong><em>DEVSEASONAL</em><strong>:</strong><em>seasonal period</em><strong>:</strong><em>gamma</em><strong>:</strong><em>rra-num</em>[<strong>:smoothing-window=</strong><em>fraction</em>]</p>
-</li>
-<li>
-<p><strong>RRA:</strong><em>DEVPREDICT</em><strong>:</strong><em>rows</em><strong>:</strong><em>rra-num</em></p>
-</li>
-<li>
-<p><strong>RRA:</strong><em>FAILURES</em><strong>:</strong><em>rows</em><strong>:</strong><em>threshold</em><strong>:</strong><em>window length</em><strong>:</strong><em>rra-num</em></p>
-</li>
-</ul>
+<li></li>
+<strong>RRA:</strong><em>HWPREDICT</em><strong>:</strong><em>rows</em><strong>:</strong><em>alpha</em><strong>:</strong><em>beta</em><strong>:</strong><em>seasonal period</em>[<strong>:</strong><em>rra-num</em>]
+<p></p>
+<li></li>
+<strong>RRA:</strong><em>MHWPREDICT</em><strong>:</strong><em>rows</em><strong>:</strong><em>alpha</em><strong>:</strong><em>beta</em><strong>:</strong><em>seasonal period</em>[<strong>:</strong><em>rra-num</em>]
+<p></p>
+<li></li>
+<strong>RRA:</strong><em>SEASONAL</em><strong>:</strong><em>seasonal period</em><strong>:</strong><em>gamma</em><strong>:</strong><em>rra-num</em>[<strong>:smoothing-window=</strong><em>fraction</em>]
+<p></p>
+<li></li>
+<strong>RRA:</strong><em>DEVSEASONAL</em><strong>:</strong><em>seasonal period</em><strong>:</strong><em>gamma</em><strong>:</strong><em>rra-num</em>[<strong>:smoothing-window=</strong><em>fraction</em>]
+<p></p>
+<li></li>
+<strong>RRA:</strong><em>DEVPREDICT</em><strong>:</strong><em>rows</em><strong>:</strong><em>rra-num</em>
+<p></p>
+<li></li>
+<strong>RRA:</strong><em>FAILURES</em><strong>:</strong><em>rows</em><strong>:</strong><em>threshold</em><strong>:</strong><em>window length</em><strong>:</strong><em>rra-num</em>
+<p></p></ul>
<p>These <strong>RRAs</strong> differ from the true consolidation functions in several ways.
First, each of the <strong>RRA</strong>s is updated once for every primary data point.
Second, these <strong>RRAs</strong> are interdependent. To generate real-time confidence
@@ -354,22 +366,21 @@ index in the order of <strong>RRA</strong> creation (that is, the order they app
in the <em>create</em> command). The dependent <strong>RRA</strong> for each <strong>RRA</strong>
requiring the <em>rra-num</em> argument is listed here:</p>
<ul>
-<li>
-<p>HWPREDICT <em>rra-num</em> is the index of the SEASONAL <strong>RRA</strong>.</p>
-</li>
-<li>
-<p>SEASONAL <em>rra-num</em> is the index of the HWPREDICT <strong>RRA</strong>.</p>
-</li>
-<li>
-<p>DEVPREDICT <em>rra-num</em> is the index of the DEVSEASONAL <strong>RRA</strong>.</p>
-</li>
-<li>
-<p>DEVSEASONAL <em>rra-num</em> is the index of the HWPREDICT <strong>RRA</strong>.</p>
-</li>
-<li>
-<p>FAILURES <em>rra-num</em> is the index of the DEVSEASONAL <strong>RRA</strong>.</p>
-</li>
-</ul>
+<li></li>
+HWPREDICT <em>rra-num</em> is the index of the SEASONAL <strong>RRA</strong>.
+<p></p>
+<li></li>
+SEASONAL <em>rra-num</em> is the index of the HWPREDICT <strong>RRA</strong>.
+<p></p>
+<li></li>
+DEVPREDICT <em>rra-num</em> is the index of the DEVSEASONAL <strong>RRA</strong>.
+<p></p>
+<li></li>
+DEVSEASONAL <em>rra-num</em> is the index of the HWPREDICT <strong>RRA</strong>.
+<p></p>
+<li></li>
+FAILURES <em>rra-num</em> is the index of the DEVSEASONAL <strong>RRA</strong>.
+<p></p></ul>
<p><em>threshold</em> is the minimum number of violations (observed values outside
the confidence bounds) within a window that constitutes a failure. If the
FAILURES <strong>RRA</strong> is implicitly created, the default value is 7.</p>
@@ -453,19 +464,20 @@ same average rate. <em>-- Don Baarda <<a href="mailto:don.baarda@baesystems.c
<h1><a name="how_to_measure">HOW TO MEASURE</a></h1>
<p>Here are a few hints on how to measure:</p>
<dl>
-<dt><strong><a name="item_temperature">Temperature</a></strong></dt>
-
+<dt><strong><a name="item_temperature">Temperature</a></strong><br />
+</dt>
<dd>
-<p>Usually you have some type of meter you can read to get the temperature.
+Usually you have some type of meter you can read to get the temperature.
The temperature is not really connected with a time. The only connection is
that the temperature reading happened at a certain time. You can use the
<strong>GAUGE</strong> data source type for this. RRDtool will then record your reading
-together with the time.</p>
+together with the time.
</dd>
-<dt><strong><a name="item_mail_messages">Mail Messages</a></strong></dt>
-
+<p></p>
+<dt><strong><a name="item_mail_messages">Mail Messages</a></strong><br />
+</dt>
<dd>
-<p>Assume you have a method to count the number of messages transported by
+Assume you have a method to count the number of messages transported by
your mailserver in a certain amount of time, giving you data like '5
messages in the last 65 seconds'. If you look at the count of 5 like an
<strong>ABSOLUTE</strong> data type you can simply update the RRD with the number 5 and the
messages transported in a day, you can get the average messages per second
from RRDtool for the day in question and multiply this number with the
number of seconds in a day. Because all math is run with Doubles, the
-precision should be acceptable.</p>
+precision should be acceptable.
</dd>
-<dt><strong><a name="item_it_27s_always_a_rate">It's always a Rate</a></strong></dt>
-
+<p></p>
+<dt><strong><a name="item_it_27s_always_a_rate">It's always a Rate</a></strong><br />
+</dt>
<dd>
-<p>RRDtool stores rates in amount/second for COUNTER, DERIVE and ABSOLUTE
+RRDtool stores rates in amount/second for COUNTER, DERIVE and ABSOLUTE
data. When you plot the data, you will get on the y axis
amount/second which you might be tempted to convert to an absolute
amount by multiplying by the delta-time between the points. RRDtool
bytes/hour, for example, or plot absolute amounts with another tool
that draws bar-plots, where the delta-time is clear on the plot for
each point (such that when you read the graph you see for example GB
-on the y axis, days on the x axis and one bar for each day).</p>
+on the y axis, days on the x axis and one bar for each day).
</dd>
-</dl>
+<p></p></dl>
<p>
</p>
<hr />