浏覽器預設對同一域下的資源，隻保持一定的連接配接數，會阻塞過多的連接配接。rfc2616建議不超過2個:
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. A proxy SHOULD use up to 2*N connections to another server or proxy, where N is the number of simultaneously active users. These guidelines are intended to improve HTTP response times and avoid congestion.
不同浏覽器的預設值不一樣，對于不同的HTTP協定其值也不一樣。見下表。
| 浏覽器 | HTTP 1.1 | HTTP 1.0 |
|---|---|---|
| IE 6,7 | 2 | 4 |
| IE 8 | 6 | 6 |
| Firefox 2 | 2 | 8 |
| Firefox 3 | 6 | 6 |
| Safari 3, 4 | 4 | 4 |
| Chrome 1,2 | 6 | ? |
| Chrome 3 | 4 | 4 |
| Opera 9.63,10.00alpha | 4 | 4 |
上表資料來自Steve Souders。
總的來看，HTTP1.0下允許的連接配接數普遍大于HTTP1.1協定下的，是因為HTTP1.1是保持連接配接的，本身對同域下資源的擷取就是優化的，且對資源的消耗要大于HTTP1.0。在rfc2616中說到，限制連接配接數的目的在于提高響應速度和避免擁塞。
修改浏覽器最大連接配接數
1. Firefox
在檔案 X:\Program Files\Mozilla Firefox\greprefs\all.js中，有如下的參數：
// if network.http.keep-alive is true, and if NOT connecting via a proxy, then
// a new connection will only be attempted if the number of active persistent
// connections to the server is less then max-persistent-connections-per-serve r.
pref("network.http.max-persistent-connections-per-server", 6);
// if network.http.keep-alive is true, and if connecting via a proxy, then a
// new connection will only be attempted if the number of active persistent
// connections to the proxy is less then max-persistent-connections-per-proxy .
pref("network.http.max-persistent-connections-per-proxy", 8);
2. IE
需要修改系統資料庫或組政策，詳情見微軟的技術支援。
轉載于:https://www.cnblogs.com/web-backend/archive/2010/05/03/1726835.html