+=item B<PreCacheChain> I<ChainName>
+
+=item B<PostCacheChain> I<ChainName>
+
+Configure the name of the "pre-cache chain" and the "post-cache chain". The
+argument is the name of a I<chain> that should be executed before and/or after
+the values have been added to the cache.
+
+To understand the implications, it's important you know what is going on inside
+I<collectd>. The following diagram shows how values are passed from the
+read-plugins to the write-plugins:
+
+ +---------------+
+ ! Read-Plugin !
+ +-------+-------+
+ !
+ + - - - - V - - - - +
+ : +---------------+ :
+ : ! Pre-Cache ! :
+ : ! Chain ! :
+ : +-------+-------+ :
+ : ! :
+ : V :
+ : +-------+-------+ : +---------------+
+ : ! Cache !--->! Value Cache !
+ : ! insert ! : +---+---+-------+
+ : +-------+-------+ : ! !
+ : ! ,------------' !
+ : V V : V
+ : +-------+---+---+ : +-------+-------+
+ : ! Post-Cache +--->! Write-Plugins !
+ : ! Chain ! : +---------------+
+ : +---------------+ :
+ : :
+ : dispatch values :
+ + - - - - - - - - - +
+
+After the values are passed from the "read" plugins to the dispatch functions,
+the pre-cache chain is run first. The values are added to the internal cache
+afterwards. The post-cache chain is run after the values have been added to the
+cache. So why is it such a huge deal if chains are run before or after the
+values have been added to this cache?
+
+Targets that change the identifier of a value list should be executed before
+the values are added to the cache, so that the name in the cache matches the
+name that is used in the "write" plugins. The C<unixsock> plugin, too, uses
+this cache to receive a list of all available values. If you change the
+identifier after the value list has been added to the cache, this may easily
+lead to confusion, but it's not forbidden of course.
+
+The cache is also used to convert counter values to rates. These rates are, for
+example, used by the C<value> match (see below). If you use the rate stored in
+the cache B<before> the new value is added, you will use the old, B<previous>
+rate. Write plugins may use this rate, too, see the C<csv> plugin, for example.
+The C<unixsock> plugin uses these rates too, to implement the C<GETVAL>
+command.
+
+Last but not last, the B<stop> target makes a difference: If the pre-cache
+chain returns the stop condition, the value will not be added to the cache and
+the post-cache chain will not be run.
+