Open connection difference in Comet and Websockets

Question

I was trying to understand the difference in Websocket and Comet model. As per my understanding,

In comet model, the connection remains opened until the server has something to push to the client. Once server pushes the data to client, the connection is closed and new connection is established for the next request. It is not considered a good approach as the connection may remain open for long time (causing intensive use of server resources) or may timeout.

On the other hand, websockets start with a handshake connection and once both the client and server agree to exchange data, the connection remains open.

So in both the case the connection remains open for long time (especially websocket). So isnt't this a drawback of websocket to keep the connection open. I would like to take the reference of SignalR in asp.net to discuss about this concept.

Answer 1

First, let's clarify that Comet comes in two flavors: HTTP Streaming and HTTP Long Polling. You were referring to Long Polling. (See this other answer for terminology).

In all three cases (WebSocket, HTTP Streaming, and HTTP Long Polling) the underlying TCP socket is kept open. That's actually the main feature of this kind of techniques and not a side effect. You want the socket to stay permanently open (I'm oversimplifying now), so that data can be pushed asynchronously and with low latency.

As you correctly said, this implies that the server must be able to handle a large number of open sockets without wasting resources. And that's one of the key elements in the choice of a good Comet/WebSocket server.