由于有用wordpress做站的冲动，就看了一下wordpress对大数据高负载时候的解决方法，看起来wordpress对高负载唯一的办法，只能是上Varnish了，特此记录一下。
Varnish要配合使用WordPress Varnish插件，还要优化配置才能够达到最好的效果，由于没有相应的站测试，只能贴一些测试。

WordPress 缓存插件性能对比

虽然原生态的 WordPress 效率实在底下，但是 WordPress 提供了很多插件，国外服务器领域里也有很多开源的缓存软件，这几天在 Jerry的帮忙下，萝卜网的服务器用上了 Varnish 缓存加速，现在每天轻松应付流量，系统的负载也不再升高，呵呵。这里贴一篇国外高手的文章，一些主流的 WordPress 缓存插件，以及和用上 Varnish 的 WordPress 性能的对比。

原文：《WordPress Cache Plugin Benchmarks》
http://cd34.com/blog/scalability/wordpress-cache-plugin-benchmarks/

译文：《WordPress 缓存插件性能对比》，译文网址已经失效。

1、作者使用的插件下载以及版本号：
DB Cache (version 0.6)
DB Cache Reloaded (version 2.0.2)
W3 Total Cache (version 0.8.5.1)
WP Cache (version 2.1.2)
WP Super Cache (version 0.9.9)
WP Widget Cache (version 0.25.2)
WP File Cache(version 1.2.5)
WP Varnish (in beta)
WP Varnish ESI Widget (in beta)

2、生产环境：
Debian 3.1/Squeeze VPS
Linux Kernel 2.6.33
Single core of a Xen Virtualized Xeon X3220 (2.40ghz)
2gb RAM
CoW file is written on a Raid-10 System using 4x1tb 7200RPM Drives
Apache 2.2.14 mpm-prefork
PHP 5.3.1
WordPress 官方主题测试数据
Tests are performed from a Quadcore Xeon machine connected via 1000 Base T on the same switch and /24 as the VPS machine

3、测试使用的Bash代码：

#!/bin/shFETCHES=1000
PARALLEL=10/usr/sbin/apache2ctl stop
/etc/init.d/mysql restart
apache2ctl start
echo Sleeping
sleep 30
time ( \
echo First Run; \
ab -n $FETCHES -c $PARALLEL http://example.com/; \
echo Second Run; \
ab -n $FETCHES -c $PARALLEL http://example.com/; \
\
echo First Run; \
./http_load -parallel $PARALLEL -fetches $FETCHES wordpresstest; \
echo Second Run; \
./http_load -parallel $PARALLEL -fetches $FETCHES wordpresstest; \
)

4、测试以下 URL 的 http_load：
http://example.com/
http://example.com/2010/03/hello-world/
http://example.com/2008/09/layout-test/
http://example.com/2008/04/simple-gallery-test/
http://example.com/2007/12/category-name-clash/
http://example.com/2007/12/test-with-enclosures/
http://example.com/2007/11/block-quotes/
http://example.com/2007/11/many-categories/
http://example.com/2007/11/many-tags/
http://example.com/2007/11/tags-a-and-c/
http://example.com/2007/11/tags-b-and-c/
http://example.com/2007/11/tags-a-and-b/
http://example.com/2007/11/tag-c/
http://example.com/2007/11/tag-b/
http://example.com/2007/11/tag-a/
http://example.com/2007/09/tags-a-b-c/
http://example.com/2007/09/raw-html-code/
http://example.com/2007/09/simple-markup-test/
http://example.com/2007/09/embedded-video/
http://example.com/2007/09/contributor-post-approved/
http://example.com/2007/09/one-comment/
http://example.com/2007/09/no-comments/
http://example.com/2007/09/many-trackbacks/
http://example.com/2007/09/one-trackback/
http://example.com/2007/09/comment-test/
http://example.com/2007/09/a-post-with-multiple-pages/
http://example.com/2007/09/lorem-ipsum/
http://example.com/2007/09/cat-c/
http://example.com/2007/09/cat-b/
http://example.com/2007/09/cat-a/
http://example.com/2007/09/cats-a-and-c/

5、最终性能对比：
Sorted in Ascending order in terms of higher overall performance

Addon Apachebench Cold Start
Warm Start http_load Cold Start
Warm Start
Req/Second Time/Request 50% within x ms Fetches/Second Min First Response Avg First Response
Baseline 4.97 201.006 2004 15.1021 335.708 583.363
5.00 200.089 2000 15.1712 304.446 583.684
DB Cache 4.80 208.436 2087 15.1021 335.708 583.363
Cached all SQL queries 4.81 207.776 2091 15.1712 304.446 583.684
DB Cache 4.87 205.250 2035 14.1992 302.335 621.092
Out of Box config 4.94 202.624 2026 14.432 114.983 618.434
WP File Cache 4.95 201.890 2009 15.8869 158.597 549.176
4.99 200.211 2004 16.1758 99.728 544.107
DB Cache Reloaded 5.02 199.387 1983 15.0167 187.343 589.196
All SQL Queries Cached 5.03 200.089 1985 14.9233 150.145 586.443
DB Cache Reloaded 5.06 197.636 1968 14.9697 174.857 589.161
Out of Box config 5.08 196.980 1968 15.181 257.533 587.737
Widgetcache 6.667 149.903 1492 15.0264 245.332 602.039
6.72 148.734 1487 15.1887 299.65 598.017
W3 Total Cache 153.45 65.167 60 133.1898 8.916 85.7177
DB Cache off, Page Caching with Memcached 169.46 59.011 57 188.4 9.107 50.142
W3 Total Cache 173.49 57.639 52 108.898 7.668 86.4077
DB Cache off, Minify Cache with Memcached 189.76 52.698 48 203.522 8.122 43.8795
W3 Total Cache 171.34 58.364 50 203.718 8.097 44.1234
DB Cache using Memcached 190.01 52.269 48 206.187 8.186 42.4438
W3 Total Cache 175.29 57.048 48 87.423 7.515 107.973
Out of Box config 191.15 52.314 47 204.387 8.288 43.217
W3 Total Cache 175.29 57.047 51 204.557 8.199 42.9365
Database Cache using APC 191.19 52.304 48 200.612 8.11 44.6691
W3 Total Cache 114.02 87.703 49 114.393 8.206 82.0678
Database Cache Disabled 191.76 52.150 49 203.781 8.095 42.558
W3 Total Cache 175.80 56.884 51 107.842 7.281 87.2761
Database Cache Disabled, Minify Cache using APC 192.01 52.082 50 205.66 8.244 43.1231
W3 Total Cache 104.90 95.325 51 123.041 7.868 74.5887
Database Cache Disabled, Page Caching using APC 197.55 50.620 46 210.445 7.907 41.4102
WP Super Cache 336.88 2.968 16 15.1021 335.708 583.363
Out of Box config, Half On 391.59 2.554 16 15.1712 304.446 583.684
WP Cache 161.63 6.187 12 15.1021 335.708 583.363
482.29 20.735 11 15.1712 304.446 583.684
WP Super Cache 919.11 1.088 3 190.117 1.473 47.9367
Full on, Lockdown mode 965.69 1.036 3 975.979 1.455 9.67185
WP Super Cache 928.45 1.077 3 210.106 1.468 43.8167
Full on 970.45 1.030 3 969.256 1.488 9.78753
W3 Total Cache 1143.94 8.742 2 165.547 0.958 56.7702
Page Cache using Disk Enhanced 1222.16 8.182 3 1290.43 0.961 7.15632
W3 Total Cache 1153.50 8.669 3 165.725 0.916 56.5004
Page Caching – Disk Enhanced, Minify/Database using APC 1211.22 8.256 2 1305.94 0.948 6.97114
Varnish ESI 2304.18 0.434 4 349.351 0.221 28.1079
2243.33 0.44689 4 4312.78 0.152 2.09931
WP Varnish 1683.89 0.594 3 369.543 0.155 26.8906
3028.41 0.330 3 4318.48 0.148 2.15063
6、总结：
Varnish 用来做缓存，因为是内存级别的，读取速度相当之快，所有其他的缓存插件都是浮云，唯一能媲美的是启用了Page Caching – Disk (Enhanced), Minify Caching – Alternative PHP Cache (APC), Database Caching – Alternative PHP Cache (APC)的 W3 Total Cache 插件。

萝卜网目前使用的方案是 Nginx （82端口） + Varnish （反向监听81）+ Nginx （再反向监听80），当然也可以尝试 Apache （82）+ Varnish（81） + Nginx （80），具体怎么配置就不是本文的讨论范围了。

至于为什么不用 Apache （81） + Nginx （80），因为 Nginx 用来做反向代理+缓存加速的话，是在硬盘读取的，而Varnish直接读取内存，速度明显加快，唯一头疼的就是太损耗内存，服务器8G的内存瞬间跑满，看来得花钱加大内存了 T_T

英文版转载

WordPress Cache Plugin Benchmarks
A lot of time and effort goes into keeping a WordPress site alive when it starts to accumulate traffic. While not every site has the same goals, keeping a site responsive and online is the number one priority. When a surfer requests the page, it should load quickly and be responsive. Each addon handles caching a little differently and should be used in different cases.

For many sites, page caching will provide decent performance. Once your sites starts receiving comments, or people log in, many cache solutions cache too heavily or not enough. As many solutions as there are, it is obvious that WordPress underperforms in higher traffic situations.

The list of caching addons that we’re testing:

* DB Cache (version 0.6)
* DB Cache Reloaded (version 2.0.2)
* W3 Total Cache (version 0.8.5.1)
* WP Cache (version 2.1.2)
* WP Super Cache (version 0.9.9)
* WP Widget Cache (version 0.25.2)
* WP File Cache(version 1.2.5)
* WP Varnish (in beta)
* WP Varnish ESI Widget (in beta)

What are we testing?
* Frontpage hits
* httpload through a series of urls

We take two measurements. The cold start measurement is taken after any plugin cache has been cleared and Apache2 and MySQL have been restarted. A 30 second pause is inserted prior to starting the tests. We perform a frontpage hit 1000 times with 10 parallel connections. We then repeat that test after Apache2 and the caching solution have had time to cache that page. Afterwards, http_load requests a series of 30 URLs to simulate people surfing other pages. Between those two measurements, we should have a pretty good indicator of how well a site is going to perform in real life.

What does the Test Environment look like?
* Debian 3.1/Squeeze VPS
* Linux Kernel 2.6.33
* Single core of a Xen Virtualized Xeon X3220 (2.40ghz)
* 2gb RAM
* CoW file is written on a Raid-10 System using 4x1tb 7200RPM Drives
* Apache 2.2.14 mpm-prefork
* PHP 5.3.1
* WordPress Theme Test Data
* Tests are performed from a Quadcore Xeon machine connected via 1000 Base T on the same switch and /24 as the VPS machine

This setup is designed to replicate what most people might choose to host a reasonably popular wordpress site.

tl;dr Results
If you aren’t using Varnish in front of your web site, the clear winner is W3 Total Cache using Page Caching – Disk (Enhanced), Minify Caching – Alternative PHP Cache (APC), Database Caching – Alternative PHP Cache (APC).

If you can use Varnish, WP Varnish would be a very simple way to gain quite a bit of performance while maintaining interactivity. WP Varnish purges the cache when posts are made, allowing the site to be more dynamic and not suffer from the long cache delay before a page is updated.

W3 Total Cache has a number of options and sometimes settings can be quite detrimental to site performance. If you can’t use APC caching or Memcached for caching Database queries or Minification, turn both off. W3 Total Cache’s interface is overwhelming but the plugin author has indicated that he’ll be making a new ‘Wizard’ configuration menu in the next version along with Fragment Caching.

WP Super Cache isn’t too far behind and is also a reasonable alternative.

Either way, if you want your site to survive, you need to use a cache addon. Going from 2.5 requests per second to 800+ requests per second makes a considerable difference in the usability of your site for visitors. Logged in users and search engine bots still see uncached/live results, so, you don’t need to worry that your site won’t be indexed properly.

Results
Sorted in Ascending order in terms of higher overall performance

Addon Apachebench Cold Start
Warm Start http_load Cold Start
Warm Start
Req/Second Time/Request 50% within x ms Fetches/Second Min First Response Avg First Response
Baseline 4.97 201.006 2004 15.1021 335.708 583.363
5.00 200.089 2000 15.1712 304.446 583.684
DB Cache 4.80 208.436 2087 15.1021 335.708 583.363
Cached all SQL queries 4.81 207.776 2091 15.1712 304.446 583.684
DB Cache 4.87 205.250 2035 14.1992 302.335 621.092
Out of Box config 4.94 202.624 2026 14.432 114.983 618.434
WP File Cache 4.95 201.890 2009 15.8869 158.597 549.176
4.99 200.211 2004 16.1758 99.728 544.107
DB Cache Reloaded 5.02 199.387 1983 15.0167 187.343 589.196
All SQL Queries Cached 5.03 200.089 1985 14.9233 150.145 586.443
DB Cache Reloaded 5.06 197.636 1968 14.9697 174.857 589.161
Out of Box config 5.08 196.980 1968 15.181 257.533 587.737
Widgetcache 6.667 149.903 1492 15.0264 245.332 602.039
6.72 148.734 1487 15.1887 299.65 598.017
W3 Total Cache 153.45 65.167 60 133.1898 8.916 85.7177
DB Cache off, Page Caching with Memcached 169.46 59.011 57 188.4 9.107 50.142
W3 Total Cache 173.49 57.639 52 108.898 7.668 86.4077
DB Cache off, Minify Cache with Memcached 189.76 52.698 48 203.522 8.122 43.8795
W3 Total Cache 171.34 58.364 50 203.718 8.097 44.1234
DB Cache using Memcached 190.01 52.269 48 206.187 8.186 42.4438
W3 Total Cache 175.29 57.048 48 87.423 7.515 107.973
Out of Box config 191.15 52.314 47 204.387 8.288 43.217
W3 Total Cache 175.29 57.047 51 204.557 8.199 42.9365
Database Cache using APC 191.19 52.304 48 200.612 8.11 44.6691
W3 Total Cache 114.02 87.703 49 114.393 8.206 82.0678
Database Cache Disabled 191.76 52.150 49 203.781 8.095 42.558
W3 Total Cache 175.80 56.884 51 107.842 7.281 87.2761
Database Cache Disabled, Minify Cache using APC 192.01 52.082 50 205.66 8.244 43.1231
W3 Total Cache 104.90 95.325 51 123.041 7.868 74.5887
Database Cache Disabled, Page Caching using APC 197.55 50.620 46 210.445 7.907 41.4102
WP Super Cache 336.88 2.968 16 15.1021 335.708 583.363
Out of Box config, Half On 391.59 2.554 16 15.1712 304.446 583.684
WP Cache 161.63 6.187 12 15.1021 335.708 583.363
482.29 20.735 11 15.1712 304.446 583.684
WP Super Cache 919.11 1.088 3 190.117 1.473 47.9367
Full on, Lockdown mode 965.69 1.036 3 975.979 1.455 9.67185
WP Super Cache 928.45 1.077 3 210.106 1.468 43.8167
Full on 970.45 1.030 3 969.256 1.488 9.78753
W3 Total Cache 1143.94 8.742 2 165.547 0.958 56.7702
Page Cache using Disk Enhanced 1222.16 8.182 3 1290.43 0.961 7.15632
W3 Total Cache 1153.50 8.669 3 165.725 0.916 56.5004
Page Caching – Disk Enhanced, Minify/Database using APC 1211.22 8.256 2 1305.94 0.948 6.97114
Varnish ESI 2304.18 0.434 4 349.351 0.221 28.1079
2243.33 0.44689 4 4312.78 0.152 2.09931
WP Varnish 1683.89 0.594 3 369.543 0.155 26.8906
3028.41 0.330 3 4318.48 0.148 2.15063
Test Script

#!/bin/sh

FETCHES=1000
PARALLEL=10

/usr/sbin/apache2ctl stop
/etc/init.d/mysql restart
apache2ctl start
echo Sleeping
sleep 30
time ( \
echo First Run; \
ab -n $FETCHES -c $PARALLEL http://example.com/; \
echo Second Run; \
ab -n $FETCHES -c $PARALLEL http://example.com/; \
\
echo First Run; \
./http_load -parallel $PARALLEL -fetches $FETCHES wordpresstest; \
echo Second Run; \
./http_load -parallel $PARALLEL -fetches $FETCHES wordpresstest; \
)

URL File for http_load

http://example.com/
http://example.com/2010/03/hello-world/
http://example.com/2008/09/layout-test/
http://example.com/2008/04/simple-gallery-test/
http://example.com/2007/12/category-name-clash/
http://example.com/2007/12/test-with-enclosures/
http://example.com/2007/11/block-quotes/
http://example.com/2007/11/many-categories/
http://example.com/2007/11/many-tags/
http://example.com/2007/11/tags-a-and-c/
http://example.com/2007/11/tags-b-and-c/
http://example.com/2007/11/tags-a-and-b/
http://example.com/2007/11/tag-c/
http://example.com/2007/11/tag-b/
http://example.com/2007/11/tag-a/
http://example.com/2007/09/tags-a-b-c/
http://example.com/2007/09/raw-html-code/
http://example.com/2007/09/simple-markup-test/
http://example.com/2007/09/embedded-video/
http://example.com/2007/09/contributor-post-approved/
http://example.com/2007/09/one-comment/
http://example.com/2007/09/no-comments/
http://example.com/2007/09/many-trackbacks/
http://example.com/2007/09/one-trackback/
http://example.com/2007/09/comment-test/
http://example.com/2007/09/a-post-with-multiple-pages/
http://example.com/2007/09/lorem-ipsum/
http://example.com/2007/09/cat-c/
http://example.com/2007/09/cat-b/
http://example.com/2007/09/cat-a/
http://example.com/2007/09/cats-a-and-c/