fixed indenting

[rrdtool.git] / doc / rrdcreate.pod

diff --git a/doc/rrdcreate.pod b/doc/rrdcreate.pod
index 3689e29..86817bd 100644 (file)
--- a/doc/rrdcreate.pod
+++ b/doc/rrdcreate.pod
@@ -173,7 +173,35 @@ data point>.
 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
+B<MIN>, B<MAX>, B<LAST>. 
+
+=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<interesting> properties of your data is kept across the aggregation
+process.
+
+
+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>
@@ -210,11 +238,11 @@ B<RRA:>I<MHWPREDICT>B<:>I<rows>B<:>I<alpha>B<:>I<beta>B<:>I<seasonal period>[B<:
 
 =item *
 
-B<RRA:>I<SEASONAL>B<:>I<seasonal period>B<:>I<gamma>B<:>I<rra-num>
+B<RRA:>I<SEASONAL>B<:>I<seasonal period>B<:>I<gamma>B<:>I<rra-num>[B<:smoothing-window=>I<fraction>]
 
 =item *
 
-B<RRA:>I<DEVSEASONAL>B<:>I<seasonal period>B<:>I<gamma>B<:>I<rra-num>
+B<RRA:>I<DEVSEASONAL>B<:>I<seasonal period>B<:>I<gamma>B<:>I<rra-num>[B<:smoothing-window=>I<fraction>]
 
 =item *
 
@@ -314,6 +342,13 @@ If SEASONAL and DEVSEASONAL B<RRAs> are created explicitly, 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<smoothing-window> specifies the fraction of a season that should be
+averaged around each point. By default, the value of I<smoothing-window> is
+0.05, which means each value in SEASONAL and DEVSEASONAL will be occasionally
+replaced by averaging it with its (I<seasonal period>*0.05) nearest neighbors.
+Setting I<smoothing-window> to zero will disable the running-average smoother
+altogether.
+
 I<rra-num> provides the links between related B<RRAs>. If HWPREDICT is
 specified alone and the other B<RRAs> are created implicitly, then
 there is no need to worry about this argument. If B<RRAs> are created
@@ -364,28 +399,24 @@ Here is an explanation by Don Baarda on the inner workings of RRDtool.
 It may help you to sort out why all this *UNKNOWN* data is popping
 up in your databases:
 
-RRDtool gets fed samples at arbitrary times. From these it builds Primary
-Data Points (PDPs) at exact times on every "step" interval. The PDPs are
-then accumulated into RRAs.
+RRDtool gets fed samples/updates at arbitrary times. From these it builds Primary
+Data Points (PDPs) on every "step" interval. The PDPs are
+then accumulated into the RRAs.
 
 The "heartbeat" defines the maximum acceptable interval between
-samples. If the interval between samples is less than "heartbeat",
+samples/updates. If the interval between samples is less than "heartbeat",
 then an average rate is calculated and applied for that interval. If
 the interval between samples is longer than "heartbeat", then that
 entire interval is considered "unknown". Note that there are other
 things that can make a sample interval "unknown", such as the rate
-exceeding limits, or even an "unknown" input sample.
+exceeding limits, or a sample that was explicitly marked as unknown.
 
 The known rates during a PDP's "step" interval are used to calculate
-an average rate for that PDP. Also, if the total "unknown" time during
-the "step" interval exceeds the "heartbeat", the entire PDP is marked
+an average rate for that PDP. If the total "unknown" time accounts for
+more than B<half> the "step", the entire PDP is marked
 as "unknown". This means that a mixture of known and "unknown" sample
-times in a single PDP "step" may or may not add up to enough "unknown"
-time to exceed "heartbeat" and hence mark the whole PDP "unknown". So
-"heartbeat" is not only the maximum acceptable interval between
-samples, but also the maximum acceptable amount of "unknown" time per
-PDP (obviously this is only significant if you have "heartbeat" less
-than "step").
+times in a single PDP "step" may or may not add up to enough "known"
+time to warrent for a known PDP.
 
 The "heartbeat" can be short (unusual) or long (typical) relative to
 the "step" interval between PDPs. A short "heartbeat" means you
@@ -417,7 +448,7 @@ same average rate. I<-- Don Baarda E<lt>don.baarda@baesystems.comE<gt>>
        u|15|/     "swt" expired
        u|16|
         |17|----* sample4, restart "hb", create "pdp" for step1 = 
-        |18|   /  = unknown due to 10 "u" labled secs > "hb"
+        |18|   /  = unknown due to 10 "u" labled secs > 0.5 * step
         |19|  /
         |20| /
         |21|----* sample5, restart "hb"