=item B<CacheFlush> I<Seconds>
-When the C<rrdtool plugin> uses a cache (by setting B<CacheTimeout>, see below)
+When the C<rrdtool> plugin uses a cache (by setting B<CacheTimeout>, see below)
it writes all values for a certain RRD-file if the oldest value is older than
(or equal to) the number of seconds specified. If some RRD-file is not updated
anymore for some reason (the computer was shut down, the network is broken,
The trade off is that the graphs kind of "drag behind" and that more memory is
used.
+=item B<WritesPerSecond> B<Updates>
+
+When collecting many statistics with collectd and the C<rrdtool> plugin, you
+will run serious performance problems. The B<CacheFlush> setting and the
+internal update queue assert that collectd continues to work just fine even
+under heavy load, but the system may become very unresponsive and slow. This is
+a problem especially if create graphs from the RRD files on the same machine,
+for example using the C<graph.cgi> script included in the
+C<contrib/collection3/> directory.
+
+This setting is designed for very large setups. Setting this option to a value
+between 25 and 80 updates per second, depending on your hardware, will leave
+the server responsive enough to draw graphs even while all the cached values
+are written to disk. Flushed values, i.E<nbsp>e. values that are forced to disk
+by the B<FLUSH> command, are B<not> effected by this limit. They are still
+written as fast as possible, so that web frontends have up to date data when
+generating graphs.
+
+For example: If you have 100,000 RRD files and set B<WritesPerSecond> to 30
+updates per second, writing all values to disk will take approximately
+56E<nbsp>minutes. Together with the flushing ability that's integrated into
+"collection3" you'll end up with a responsive and fast system, up to date
+graphs and basically a "backup" of your values every hour.
+
=back
=head2 Plugin C<sensors>