Improve docs

Author: michaelklishin

docs/rabbitmq.config.example

@@ -236,8 +236,18 @@
 
    %% Fraction of the high watermark limit at which queues start to
    %% page message out to disc in order to free up memory.
+   %% For example, when vm_memory_high_watermark is set to 0.4 and this value is set to 0.5,
+   %% paging can begin as early as when 20% of total available RAM is used by the node.
    %%
-   %% Values greater than 0.9 can be dangerous and should be used carefully.
+   %% Values greater than 1.0 can be dangerous and should be used carefully.
+   %%
+   %% One alternative to this is to use durable queues and publish messages
+   %% as persistent (delivery mode = 2). With this combination queues will
+   %% move messages to disk much more rapidly.
+   %%
+   %% Another alternative is to configure queues to page all messages (both
+   %% persistent and transient) to disk as quickly
+   %% as possible, see http://www.rabbitmq.com/lazy-queues.html.
    %%
    %% {vm_memory_high_watermark_paging_ratio, 0.5},