一、 Kepp-Alive使用情况
1、当你的Server内存充足时,KeepAlive =On还是Off对系统性能影响不大。
2、当你的Server上静态网页(Html、图片、Css、Js)居多时,建议打开KeepAlive 。
3、当你的Server多为动态请求(因为连接数据库,对文件系统访问较多),KeepAlive 关掉,会节省一定的内存,节省的内存正好可以作为文件系统的Cache(vmstat命令中cache一列),降低I/O压力。
PS:当KeepAlive =On时,KeepAliveTimeOut的设置其实也是一个问题,设置的过短,会导致Apache 频繁建立连接,给Cpu造成压力,设置的过长,系统中就会堆积无用的Http连接,消耗掉大量内存,具体设置多少,可以进行不断的调节,因你的网站浏览和服务器配置 而异。
二、浏览器对Keep-Alive的并发数情况及域名开销
对于HTTP/1.0来说可以充分利用浏览器默认最大并发连接数比HTTP/1.1多的好 处,实现不增加新域名的开销而更高的并行下载,减少域名解释的开销(注:IE 6,7在HTTP/1.0中默认最大并发连接数为4,在HTTP/1.1中默认最大并发连接数为2,IE8都为6,Firefox2在HTTP/1.0中 默认最大并发连接数为2 在HTTP/1.1中默认最大并发连接数为8,firefox 3默认都是6),根据10年7月Google索引的42亿个网页的统计报告,每张网页里包含29.39个图片,7.09个外部脚本,3.22个外部CSS 样式表,如果设置了Keep-Alive并且合理控制Keep-Alive TimeOut这个参数可以大量的节约连接的开销,提高相应速度。如果设置不好,在大并发的情况小,因维持大量连接而使服务器资源耗尽,而对于目前国内大 部分的用户使用的还是IE6,7的情况
三、使用Node.js的http.Agent开发一个真正的Keep-Alive代理
/**
* Created by Administrator on 14-4-30.
*/
var http = require('http');
var EventEmitter = require('evnets').EventEmitter;
var net = require('net');
var util = require('util');
var Agent = function(optinos)
{
var self = this;
// 选项配置
self.options = options || {};
// 保存请求的全部hostname
self.requests = {};
// 创建的socket连接数
self.sockets = {};
// 未被使用的socket
self.unusedSockets = {};
// socket的最大连接数量
self.maxSockets = self.options.maxSockets || Agent.defaultMaxSockets;
self.on('free',function(socket,host,port){
var hostname = host + ':' + port;
// 如果有正在请求的主机
if(self.requests[hostname] && self.requests[hostname].length)
{
self.requests[hostname].shift().onSocket(socket);
}
else
{
// 如果没有请求数就销毁socket连接并从连接池移除
if(!self.unusedSockets[hostname])
{
self.unusedSockets[hostname] = [];
}
self.unusedSockets[hostname].push(socket);
}
});
self.createConnection = net.createConnection;
};
util.inherits(Agent,EventEmitter);
Agent.defaultMaxSockets = 10;
Agent.prototype.defaultPort = 80;
Agent.prototype.addRequest = function(req,host,port)
{
var hostname = host + ':' + port;
if(this.unusedSockets[hostname] && this.unusedSockets[hostname].length)
{
req.onSocket(this.unusedSockets[hostname].shift());
return;
}
if(!this.sockets[hostname])
{
this.sockets[hostname] = [];
}
if(this.sockets[hostname].length < this.maxSockets)
{
req.onSocket(this.createSocket(hostname,host,port));
}
else
{
if(!this.requests[hostname])
{
this.requests[hostname] = [];
}
this.requests[hostname].push(req);
}
};
Agent.prototype.createSocket = function(name, host, port) {
var self = this;
var s = self.createConnection(port, host, self.options);
if (!self.sockets[name]) {
self.sockets[name] = [];
}
this.sockets[name].push(s);
var onFree = function() {
self.emit('free', s, host, port);
}
s.on('free', onFree);
var onClose = function(err) {
// 这是唯一移除socket代理的地方,如果你想从连接池中移除socket,就关闭连接,所有的socket错误会导致连接关闭
self.removeSocket(s, name, host, port);
}
s.on('close', onClose);
var onRemove = function() {
// We need this function for cases like HTTP "upgrade"
// (defined by WebSockets) where we need to remove a socket from the pool
// because it'll be locked up indefinitely
self.removeSocket(s, name, host, port);
s.removeListener('close', onClose);
s.removeListener('free', onFree);
s.removeListener('agentRemove', onRemove);
}
s.on('agentRemove', onRemove);
return s;
};
Agent.prototype.removeSocket = function(s, name, host, port) {
if (this.sockets[name]) {
var index = this.sockets[name].indexOf(s);
if (index !== -1) {
this.sockets[name].splice(index, 1);
}
} else if (this.sockets[name] && this.sockets[name].length === 0) {
delete this.sockets[name];
delete this.requests[name];
}
if (this.requests[name] && this.requests[name].length) {
// If we have pending requests and a socket gets closed a new one
// needs to be created to take over in the pool for the one that closed.
this.createSocket(name, host, port).emit('free');
}
};
如何使用:
var http = require('http');
var keepAliveAgent = require('./agent.js');
var agent = new keepAliveAgent({ maxSockets: 100 });
// Optionally define more parallel sockets
var options = {
agent: agent,
hostname: 'example.com',
path: '/path'};
// do get
http.get(options);
// do request
http.request(options,function(){});
来源:oschina
链接:https://my.oschina.net/u/153403/blog/261105