Varnish是一款高性能的缓存加速器，Varnish把数据存放在服务器的内存中，利用内存可以极大的提高PHP页面执行速度，可以设置0～60秒的精确缓存时间，32位的机器支持的缓存文件最大为2 GB。

Varnish采用VCL的配置，而且具有强大的管理功能，如top、stat、admin、lis，管理方式比较灵活。Varnish的状态机设计不仅巧妙，结构也很清晰，利用二叉堆管理缓存文件，即可达到随时删除的目的。

Memcached是一个高性能的分布式内存对象缓存系统，通过在内存中缓存数据和对象来减少读取数据库的次数，从而提高动态、数据库驱动网站的速度。Memcached对于减少MysqL数据查询压力非常有帮助。

由于Varnish采用了Visual Page Cache技术，所有缓存的数据都直接从内存读取，而Squid从硬盘读取缓存的数据，所以Varnish在访问速度方面会更快一些。但是Varnish在高并发状态下，CPU、I/O和内存等资源的开销高于Squid。

目前Varnish3.0版本解决了服务器重启后Varnish缓存消失的问题，性能优化上有了更大的提升。本篇文章就来分享一下利用Varnish和Memcached缓存来给Wordpress加速，因为要用到内存，所以比较适合那些大内存的服务器。

用Varnish和Memcached缓存给Wordpress网站提速-内存级加速

一、Varnish安装方法

1、Varnish官网：

官方网站：https://www.varnish-cache.org/

2、对于Centos 5的，可以执行以下命令来安装：

rpm --nosignature -i http://repo.varnish-cache.org/redhat/varnish-3.0/el5/noarch/varnish-release/varnish-release-3.0-1.el5.centos.noarch.rpm

yum install varnish

3、对于是Centos 6的，可以执行以下命令来安装：

rpm --nosignature -i http://repo.varnish-cache.org/redhat/varnish-3.0/el6/noarch/varnish-release/varnish-release-3.0-1.el6.noarch.rpm

yum install varnish

4、如果版本搞错，就会出现如下提示错误：

error: Failed dependencies:

    rpmlib(FileDigests) <= 4.6.0-1 is needed by varnish-release-3.0-1.el6.noarch

    rpmlib(PayloadIsXz) <= 5.2-1 is needed by varnish-release-3.0-1.el6.noarch

Error: Missing Dependency: libedit.so.0 is needed by package varnish-3.0.5-1.el5.centos.i386 (varnish-3.0)

5、Centos 5安装时还会提示有依赖关系不能解决，解决的办法就是添加扩展的YUM 源，执行以下命令：

rpm -ivh http://apt.sw.be/redhat/el5/en/i386/rpmforge/RPMS/rpmforge-release-0.5.1-1.el5.rf.i386.rpm （32位）

rpm -ivh http://apt.sw.be/redhat/el5/en/x86_64/rpmforge/RPMS/rpmforge-release-0.5.2-2.el5.rf.x86_64.rpm （64位）

yum clean allyum update

6、对于是Debian系统，可以执行以下命令来安装：

curl http://repo.varnish-cache.org/debian/GPG-key.txt | apt-key add -echo "deb http://repo.varnish-cache.org/debian/ wheezy varnish-3.0" >> /etc/apt/sources.list

apt-get update

apt-get install varnish

6、对于是Ubuntu系统，可以执行以下命令来安装：

curl http://repo.varnish-cache.org/debian/GPG-key.txt | sudo apt-key add -echo "deb http://repo.varnish-cache.org/ubuntu/ precise varnish-3.0" | sudo tee -a /etc/apt/sources.listsudo

apt-get updatesudo

apt-get install varnish

7、设置Varnish开机启动，执行：chkconfig varnish on和chkconfig varnishncsa on

8、启动Varnish的命令是：service varnish start和service varnishncsa start

二、Varnish相关配置

1、设置好Varnish缓存规则。默认是/etc/varnish/default.vcl，大家可以下载这个Varnish WordPress配置文件覆盖原来的，地址：http://centos.googlecode.com/files/default.vcl。源码内容：

• # This is a basic VCL configuration file for varnish.  See the vcl(7)
• # man page for details on VCL syntax and semantics.
• # Default backend definition.  Set this to point to your content
• # server.
• backend default {
• .host = "127.0.0.1";
• .port = "8080";
• }
• acl purge {
• "localhost";
• "127.0.0.1";
• }
• # Below is a commented-out copy of the default VCL logic.  If you
• # redefine any of these subroutines, the built-in logic will be
• # appended to your code.
• sub vcl_recv {
• # Only cache the following site
• if (req.http.host ~ "(amhg.freehao123.info)") {
• set req.backend = default;
• } else {
• return (pass);
• }
• if (req.request == "PURGE") {
• if (!client.ip ~ purge) {
• error 405 "Not allowed.";
• }
• return (lookup);
• }
• if (req.restarts == 0) {
• if (req.http.x-forwarded-for) {
• set req.http.X-Forwarded-For =
• req.http.X-Forwarded-For + ", " + client.ip;
• } else {
• set req.http.X-Forwarded-For = client.ip;
• }
• }
• if (req.request != "GET" &&
• req.request != "HEAD" &&
• req.request != "PUT" &&
• req.request != "POST" &&
• req.request != "TRACE" &&
• req.request != "OPTIONS" &&
• req.request != "DELETE") {
• /* Non-RFC2616 or CONNECT which is weird. */
• return (pipe);
• }
• if (req.request != "GET" && req.request != "HEAD") {
• /* We only deal with GET and HEAD by default */
• return (pass);
• }
• if (req.http.Authorization || req.http.Cookie ~ "wordpress_logged" || req.http.Cookie ~ "comment_") {
• /* Not cacheable by default */
• return (pass);
• }
• return (lookup);
• }
• sub vcl_pipe {
• # Note that only the first request to the backend will have
• # X-Forwarded-For set.  If you use X-Forwarded-For and want to
• # have it set for all requests, make sure to have:
• # set bereq.http.connection = "close";
• # here.  It is not set by default as it might break some broken web
• # applications, like IIS with NTLM authentication.
• return (pipe);
• }
• sub vcl_pass {
• return (pass);
• }
• sub vcl_hash {
• hash_data(req.url);
• if (req.http.host) {
• hash_data(req.http.host);
• } else {
• hash_data(server.ip);
• }
• return (hash);
• }
• sub vcl_hit {
• if (req.request == "PURGE") {
• purge;
• error 200 "Purged.";
• }
• return (deliver);
• }
• sub vcl_miss {
• if (req.request == "PURGE") {
• purge;
• error 200 "Purged.";
• }
• return (fetch);
• }
• sub vcl_fetch {
• if (beresp.ttl <= 0s ||
• beresp.http.Set-Cookie ||
• beresp.http.Vary == "*") {
• /*
• * Mark as "Hit-For-Pass" for the next 2 minutes
• */
• set beresp.ttl = 120 s;
• return (hit_for_pass);
• }
• set beresp.ttl = 1d;
• return (deliver);
• }
• sub vcl_deliver {
• return (deliver);
• }
• sub vcl_error {
• set obj.http.Content-Type = "text/html; charset=utf-8";
• set obj.http.Retry-After = "5";
• synthetic {"
• <?xml version="1.0" encoding="utf-8"?>
• <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
• "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
• <html>
• <head>
• <title>"} + obj.status + " " + obj.response + {"</title>
• </head>
• <body>
• <h1>Error "} + obj.status + " " + obj.response + {"</h1>
• <p>"} + obj.response + {"</p>
• <h3>Guru Meditation:</h3>
• <p>XID: "} + req.xid + {"</p>
• <hr>
• <p>Varnish cache server</p>
• </body>
• </html>
• "};
• return (deliver);
• }
• sub vcl_init {
• return (ok);
• }
• sub vcl_fini {
• return (ok);
• }

2、下载下来的default.vcl你需要调整的地方有一处，就是将域名更改为自己要使用Varnish缓存的域名。

3、另外default.vcl还设置缓存时间，单位是s(秒)，h(小时),d(天)。

4、配置Varnish的访问端口。Varnish配置默认的访问端口不是80端口，因此需要修改/etc/sysconfig/varnish配置文件，把端口设置为80。

5、在/etc/sysconfig/varnish这个文件中还可以设置Varnish缓存大小，默认是1GB。