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Max parallel HTTP connections in a browser?

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How many parallel requests can Chrome handle?

Chrome has a limit of 6 connections per host name, and a max of 10 connections. This essentially means that it can handle 6 requests at a time coming from the same host, and will handle 4 more coming from another host at the same time.

What are parallel connections HTTP?

HTTP allows clients to open multiple connections and perform multiple HTTP transactions in parallel, as sketched in Figure 4-11. In this example, four embedded images are loaded in parallel, with each transaction getting its own TCP connection. Figure 4-11. Each component of a page involves a separate HTTP transaction.

What is browser limit?

Review the maximum browser connections limit to ensure optimal efficiency. Browsers have a maximum number of connections they can open per server/proxy. For example, Chrome has six available connections.

What is concurrent connection limit?

Concurrent Connection: The maximum amount of simultaneous connections your server can handle.


Max Number of default simultaneous persistent connections per server/proxy:

Firefox 2:  2
Firefox 3+: 6
Opera 9.26: 4
Opera 12:   6
Safari 3:   4
Safari 5:   6
IE 7:       2
IE 8:       6
IE 10:      8
Edge:       6
Chrome:     6

The limit is per-server/proxy, so your wildcard scheme will work.

FYI: this is specifically related to HTTP 1.1; other protocols have separate concerns and limitations (i.e., SPDY, TLS, HTTP 2).


HTTP/1.1

IE 6 and 7:      2
IE 8:            6
IE 9:            6
IE 10:           8
IE 11:           8
Firefox 2:       2
Firefox 3:       6
Firefox 4 to 46: 6
Opera 9.63:      4
Opera 10:        8
Opera 11 and 12: 6
Chrome 1 and 2:  6
Chrome 3:        4
Chrome 4 to 23:  6
Safari 3 and 4:  4

source: http://p2p.wrox.com/book-professional-website-performance-optimizing-front-end-back-end-705/

HTTP/2(SPDY)

Multiplexed support(one single TCP connection for all requests)

 BrowserVersion | ConnectionsPerHostname | MaxConnections
----------------------------------------------------------
 Chrome34/32    | 6                      | 10
 IE9            | 6                      | 35
 IE10           | 8                      | 17
 IE11           | 13                     | 17
 Firefox27/26   | 6                      | 17
 Safari7.0.1    | 6                      | 17
 Android4       | 6                      | 17
 ChromeMobile18 | 6                      | 16
 IE Mobile9     | 6                      | 60

The first value is ConnectionsPerHostname and the second value is MaxConnections.

Source: http://www.browserscope.org/?category=network&v=top

Note: ConnectionsPerHostname is the maximum number of concurrent http requests that browsers will make to the same domain. To increase the number of concurrent connections, one can host resources (e.g. images) in different domains. However, you cannot exceed MaxConnections, the maximum number of connections a browser will open in total - across all domains.

2020 Update

Number of parallel connections per browser

| Browser              | Connections per Domain         | Max Connections                |
| -------------------- | ------------------------------ | ------------------------------ |
| Chrome 81            | 6 [^note1]                     | 256[^note2]                    |
| Edge 18              | *same as Internet Explorer 11* | *same as Internet Explorer 11* |
| Firefox 68           | 9 [^note1] or 6 [^note3]       | 1000+[^note2]                  |
| Internet Explorer 11 | 12 [^note4]                    | 1000+[^note2]                  |
| Safari 13            | 6 [^note1]                     | 1000+[^note2]                  |
  • [^note1]: tested with 72 requests , 1 domain(127.0.0.1)
  • [^note2]: tested with 1002 requests, 6 requests per domain * 167 domains (127.0.0.*)
  • [^note3]: when called in async context, e.g. in callback of setTimeout, + requestAnimationFrame, then...
  • [^note4]: of which the last 6 are follow-ups (2,4,6 available at 0.5s,1s,1.5s respectively)

Various browsers have various limits for maximum connections per host name; you can find the exact numbers at http://www.browserscope.org/?category=network and here is an interesting article about connection limitations from web performance expert Steve Souders http://www.stevesouders.com/blog/2008/03/20/roundup-on-parallel-connections/