Phoenix LiveView Phoenix.Sync.LiveView.sync_stream evaluation

Issue で言及されているエントリポイント Phoenix.Sync.LiveView.sync_stream と sync_stream_update から始め、dead render、初回の live render、snapshot の経過時間、limit オプションがどのように扱われているかを追跡します。観測された動作を、要求されている現在の初期データ、最新の dead-render データ、設定可能な snapshot 更新、機能する limit と比較します。この issue では具体的なファイルやテストは指定されていません。

Hello 👋🏻

I'm evaluating Phoenix.Sync.LiveView.sync_stream in my Phoenix LiveView application. Particular use case I'm checking is notification stream - I want to display notifications and keep them up to date in the UI.

I'm using it in the "standard" way:

defmodule MyWeb.MyLive do
  use Phoenix.LiveView
  import Phoenix.Sync.LiveView

  def mount(_params, _session, socket) do
    {:ok, sync_stream(socket, :todos, Todos.Todo)}
  end

  def handle_info({:sync, event}, socket) do
    {:noreply, sync_stream_update(socket, event)}
  end
end

After playing with it for some time, I have these observations that surprised me.

1. dead render always has no data in stream - it's not ideal in tests and differs from the original LiveView approach.
2. initial live render stream has old (sometimes very old) data. It means there's a lot of catching up to be done on each page refresh (since I'm not using client-side caching)
3. Limit query seems to be not working, it silently ignores it.

So my questions:

1. Regular phoenix applications are being "mounted" frequently, on each page navigation. Currently it means each such mount is followed by a lot of catching up, which is visible in UI. I understand it's done that way to reduce database load, but it's not ideal. Is there an easy option to configure max snapshot age before it's refreshed?

2. Is there a way to get similar behaviour to phoenix streams in tests? I'm asking about dead render having fresh data (without cache)

3. Is there a way to respect limit query in the initial render? Phoenix.Sync.LiveView.sync_stream(.., ..,.., limit: 10) doesn't seem to work.

In general, I have a feeling that sync_stream is promising, but not yet battle-tested utility. Which is a shame.

What I was hoping for:

I would love a solution that would work in the same way as "stock" phoenix live view streams

1. initial data is always "current", present for both dead and initial live render, so there's not a lot of catching up, with limits working
2. I don't have to "babysit" these streams with lots of pubsub broadcasts and subscribes, it would just stay synchronized out of the box.

All in all, I'm rooting for this project! It's really impressive how it's all working, just wanted to drop my own observations.