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Building Real-time Applications with Phoenix & Elixir

Keep Channels Asynchronous

Explore how to keep Phoenix Channels asynchronous to avoid performance bottlenecks in real-time Elixir apps. Understand how spawning linked Tasks with socket references enables concurrent message handling. Learn to identify and fix slow channel processes by offloading work, improving throughput and user experience. This lesson helps you optimize real-time message processing efficiently.

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Asynchronous channels

Elixir is a parallel execution machine. Each Channel can leverage the principles of OTP design to execute work in parallel with other Channels since the BEAM executes multiple processes at once. Every message processed by a Channel, whether incoming or outgoing, must go through the Channel process to execute. This can stop working well if we’re not careful about how our Channel is designed. This is easiest to see when we have an example of the problem in front of us.

We’ll leverage our existing StatsChannel to see the effect of process slowness. Let’s add a new message handler that responds very slowly.

Elixir
# hello_sockets/lib/hello_sockets_web/channels/stats_channel.ex
  def handle_in("slow_ping", _payload, socket) do
    Process.sleep(3_000)
    {:reply, {:ok, %{ping: "pong"}}, socket}
  end

We have copied our existing ping handler but have ensured that every request takes a full three seconds to ...