Do all GWT browsers have a 2 connection limit?

Question

We have a GWT app which implements a Server Push technique to allow the server to notify the client of events. In Internet Explorer 7 we experience some performance issues which we believe to be caused by the 2 connection limit.

Reading this article http://code.google.com/docreader/#p=google-web-toolkit-incubator&s=google-web-toolkit-incubator&t=ServerPushFAQ under the section 2 Connection Limit is the statement

All GWT-compatible browsers will only make 2 connections to 1 server

Is this true? I thought most modern browsers would allow 6 connections - Is there some additional constraint on the number of open connections imposed by GWT that will restrict it to 2 even if the browser will support 6?

Answer 1

All modern browsers (2009 and later) make 6 connections per server. It's certainly possible that GWT itself imposes a limit on XHR/AJAX calls made using their APIs to avoid blocking behavioral differences across browsers.

Answer 2

GWT does not impose any limit (note that it says "GWT-compatible browsers", not "GWT"); it's just that this doc is out of date (and the whole "incubator" project deprecated, BTW)

Answer 3

Internet explorer from versiuon 5 to to has a two connection limit See:

• The Dreaded 2 Connection Limit (a comment form Anders Both not the most reliable sopurce i know...)
• Browserscope (if it is working)

You can try to only compile not for IE 6 and 7 (See: How do I speed up the gwt compiler?)

The other posibilty would be to host them on different domain names, which would allow tow connections to each domain name, as stated in your article:

A google maps application could for example load the map images from img.maps.google.com instead of maps.google.com. The browser would perceive the two hosts as different and thus allow 2 connections to each, even if they both resolve to the same IP address (=go to the same physical server machine).