title: RabbitMQ + Memory Limits
body: <p>I'm just looking in to the config details of RabbitMQ and came across</p>
  
  <pre><code>[{rabbit, [{vm_memory_high_watermark, 0}, 
             {disk_free_limit, {mem_relative, 1.0}}
            ]
  }]
  </code></pre>
  
  <p>What does this config mean?</p>
  
  <p><code>vm_memory_high_watermark</code> set to 0 means => Block all publishers immediately the rabbitmq app starts? But we still see rabbitmq able to queue whatever msgs we send. </p>
  
  <pre><code>16720 rabbitmq  20   0  142m  62m 2408 S    0  **1.6**   0:06.88 beam.smp
  </code></pre>
  
  <p>Whenever we send msgs to the broker we se this process' memory usage increasing. So, Does this mean the msgs are in memory although the watermark is set to 0? </p>
  
  <p>We are curious to know what happens if the mem limit of ram reaches and still msgs are being sent? Either publishers are blocked? or The messages are swapped out to disk if available?</p>