What does it really means by maximum concurrent connections in browser?

Question

Let's say I have a chat app with registration and it does long-polling to an Apache server. I've done some reading but I'm still confused and want to be extremely sure. From my understanding, it can either be :

1. Any amount of client can do long-polling to that server and it won't affect the limit because all the clients only have 1 concurrent connection each to the server. So if I open the chat app in 7 IE8/chrome/firefox in d same computer OR in different computer EACH and connect to the same url/domain, it won't be affected but if I open the chat in 7 tabs in IE8/chrome/firefox only then it will be affected.
2. Same as the above but the limit will only be affected if I open 7 IE8/chrome/firefox browsers in 7 computers by 7 different accounts. Which means only 6 different users can connect to the chat app at the same time.

I'm leaning heavily to the first one. Can you help me correct/expand on either both or if both are wrong, kindly add number 3? Thank you!

Answer 1

This limitation is a restriction put in place by each browser vendor. The typical connection limit for a browser instance is set to 6 socket connections to the same domain. These six connections make up the browsers socket pool. This socket pool is managed by the socket pool manager and are used across all browser processes. This is to maximize the efficiency of the TCP connection by reusing established connections, as well as other performance benefits.

According to the HTTP 1.1 specification the maximum number of connections should be limited to 2.

Clients that use persistent connections SHOULD limit the number of simultaneous connections that they maintain to a given server. A single-user client SHOULD NOT maintain more than 2 connections with any server or proxy. These guidelines are intended to improve HTTP response times and avoid congestion.

However, this spec was approved in June 1999 during the infancy of the internet, and browser vendors like Chrome have since increased this number to six.

Currently these are set to 32 sockets per proxy, 6 sockets per destination host, and 256 sockets per process (not implemented exactly correct, but good enough).

With that said, each socket pool is managed by each browser. Depending on the browsers connection limit (a minimum of two). You should be able to open 8 connections by opening two tabs in IE, Chrome, Firefox, and Safari. Your max connection is limited by the browser itself. Also keep in mind the server can only handle so many concurrent connections at once. Don't accidentally DoS yourself :)

If you absolutely need to go beyond the connection limitation you could look into domain sharding. Which basically tricks the browser into opening new more connections by providing a different the host name with the request. I wouldn't advise using it though, as the browser has set these limitations to maximize performance and reuse existing connections. Tread lightly.