PHP SSE vs PHP WebSockets(Ratchet)

Question

I will start developing a multiplayer card game in a few weeks and until then, I am doing research on the best techniques available. I will be using PHP+MySQL for server-side and JS/HTML5 for client side. The game will be also be played from mobile browser.

The gameplay of my game involves 4 or more users playing at a table, each having up to 30 seconds to take an action. There will be multiple tables available and an user can play at more than 1 table at the same time.

From my research it would seem easy to sync the client with the server by having the server push data trough SSE each time another player made an action. Then when the current player takes an action, the request data would be sent through XMLHttpRequest from client to server and then synced to other players through SSE.

Now from what I read, there is a big downfall to this because for each player that listens to the SSE process, a connection stays opened on the server, consuming a lot of memory. The application that I will build is intended to support over 10000 players on a dedicated server with modern hardware(8core CPU,64GB RAM), with time. Some may say PHP is not good for this, but the debate here is how to use PHP to make this work.

The alternative to the SSE implementation would be to use Websockets (I am currently checking Ratchet and managed to set up the Chat server from the doc), but overall I have some dillemas which prevent me from taking a decision:

1. Websockets: When establishing the handshake, a connection stays open on the server too, same as in SSE, but I guess that this is a different type of connection which consumes less memory. Is that right? So websockets would be more efficient. Any estimates on memory usage for both SSE and WebSockets? I read somewhere that each connection through SSE would consume around 20mb with APACHE and PHP. That's going to be 200GB for 10000 users (too much). I hope I am wrong.I dont know how much memory a socket connection would consume. An idle one I mean.

2. Will SSE consume more battery (on mobile phones) and will cause more web traffic than the sockets connection?

3. SSE: If an user will be playing at two tables, do I need to open two SSE processes (one for each table) or how do I tell the SSE process if I am requesting data for table1 or table2? Or I am forced to receive data for all tables at the same time? It wouldnt be a problem to receive data for all the tables that the user is now active at, but I am curious if there are ways of customizing this.

4. How about dealing with people that have unstable internet connection? Does websockets support automatic reconnection? Or this needs to be done manually from the client?

Answer 1

1) Do both WebSockets and SSEs keep the connection open?

Yes. Both WebSockets and SSEs keep the connection open as long as the server is configured to do so or connection is closed by either client or server. Because many times, servers are default configured to close the connection when it's idle for more than the time specified in configuration.

2) If both keeps the connection open then do both have same memory consumption and network overhead? Which one is lighter and faster?

First thing is that both seems to share same resources in terms of connection making because both has to handshake for the first time and check the heart beat by pinging and rest is a normal single TCP connection.

But there is an important point to note that Websocket is Bi-Directional and SSEs are Uni-Directional so even if a SSE connection is alive and you have to send some data from client to server then you will have to use some kind of XHR which will again create another connection to server. And creating connections is resource intensive. So, it seems like WebSockets is better at resource utilizing when this is about Bi-Directional like in case of above OP case of Card Game of multiplayers. And also this makes WebSockets more faster and Lighter than SSEs. SSEs are good when you just have to send data from server to clients like some Stock Market Prices, Game Scores etc.

3) If the your preferred choice is WebSocket then do we need to worry about URL Rewrite, Response Headers etc

I don't think so because if WebSockets are used with PHP then most of the time it is CLi based separate PHP Script twith a websocket connecting to something like ws://example.com:8092/websocket.php. So, I don't think there will be more to worry about URL Rewrite or response headers. And also as I think headers can be added/modified by PHP script itself if needed anyway.

4) Will SSE consume more battery (on mobile phones) and will cause more web traffic than the sockets connection?

I don't think SSE will consume more battery as compare to WebSockets. But yes it will definitely create more traffic to server because as mentioned above that SSE is Uni-Directional and each data from Client to Server will create another connection to server.

5) How about dealing with people that have unstable internet connection? Does websockets support automatic reconnection? Or this needs to be done manually from the client?

Well there are some techniques which can handle this part to reconnect in such conditions.