title: How to make sure fluentd BufferedOutput write(chunk) process events exactly once
body: <p>In a BufferedOutput plugin, 
  if <code>write(chunk)</code> throws exception or the fluentd process dies when it is processing the chunk, according to the docs it says the chunk will still stay in the queue but does that mean the events/records processed before the crash will be processed again after fluentd restarts?</p>
  
  <p>If that is the case, <code>write(chunk)</code> has to be atomic for "exactly once processing". Then, is the method written <a href="http://docs.fluentd.org/articles/plugin-development#filterstream-method" rel="nofollow">here</a> in the filterstream-method section  good for the purpose? i.e. Are the events in the <code>MultiEventStream</code> being processed atomically?</p>