Improve background_gc docs in example config files

To make it clearer that memory breakdown analysis must
be done formed. "Don't guess, collect data".

Author: michaelklishin

docs/rabbitmq.conf.example

@@ -424,11 +424,15 @@
 ##
 # queue_index_embed_msgs_below = 4kb
 
-## Whether or not to enable background periodic GC of all
-## Erlang processes in "waiting" state.
+## Whether or not to enable background periodic forced GC runs for all
+## Erlang processes on the node in "waiting" state.
 ##
 ## Disabling background GC may reduce latency for client operations,
-## keeping it enabled may reduce median RAM usage.
+## keeping it enabled may reduce median RAM usage by the binary heap
+## (see https://www.erlang-solutions.com/blog/erlang-garbage-collector.html).
+## 
+## Before trying this option, please take a look at the memory
+## breakdown (http://www.rabbitmq.com/memory-use.html).
 ##
 # background_gc_enabled = false
 

docs/rabbitmq.config.example

@@ -471,7 +471,15 @@
    %%
    %% {disk_monitor_failure_retry_interval, 120000},
 
-   %% Whether or not to enable background GC.
+   %% Whether or not to enable background periodic forced GC runs for all
+   %% Erlang processes on the node in "waiting" state.
+   %%
+   %% Disabling background GC may reduce latency for client operations,
+   %% keeping it enabled may reduce median RAM usage by the binary heap
+   %% (see https://www.erlang-solutions.com/blog/erlang-garbage-collector.html).
+   %%
+   %% Before enabling this option, please take a look at the memory
+   %% breakdown (http://www.rabbitmq.com/memory-use.html).
    %%
    %% {background_gc_enabled, false},