title: What's "tcp-backlog" in redis.conf
body: <p>I'm confused by <code>tcp-backlog</code> in redis.conf:</p>
  
  <pre><code># TCP listen() backlog.
  #
  # In high requests-per-second environments you need an high backlog in order
  # to avoid slow clients connections issues. Note that the Linux kernel
  # will silently truncate it to the value of /proc/sys/net/core/somaxconn so
  # make sure to raise both the value of somaxconn and tcp_max_syn_backlog
  # in order to get the desired effect.
  tcp-backlog 511
  </code></pre>
  
  <p>Is <code>tcp-backlog</code> the size of  "complete connection queue" (three-way handshake complete, what is described <a href="http://veithen.github.io/2014/01/01/how-tcp-backlog-works-in-linux.html" rel="noreferrer">here</a>) or "incomplete connection queue"?</p>
  
  <p>If it means "complete connection queue" then why should I raise <code>tcp_max_syn_backlog</code> which limits the size of an incomplete connection queue?</p>