出自：http://www.wealink.com/hp_post_view.htm?postId=28450&handled=

Three word expressions are common in English. Practicing them and using them when you speak will help you sound more natural. Here are several common expressions, along with an explanation and example sentence. black and white = something which is extremely clear（黑白分明的；绝对的）
He told her in black and white that she couldn't leave the house while he was out.
dos and don'ts = the rules （行为准则，须知，注意事项）
There are various dos and don'ts about driving in the UK.
haves and have nots = people who are rich and those who are not （富人和穷人）
In London you can find the haves and have nots of the population.
ins and outs = the details （细节，始末，详情）
I don't know the ins and outs of the situation, so I can't really advise you.
kiss and tell = when someone sells a story of themselves and a famous person （泄漏秘密）
The British tabloids are famous for publishing kiss and tell stories.
odds and ends = small pieces of various items （零碎东西，零星杂物）
She made a stew with the odds and ends she found in the fridge.
P's and Q's = manners ( such as please and thank you ) （言行）
Mind your P's and Q's when you visit them!
pros and cons = advantages and disadvantages （赞成和反对）
There are a few pros and cons that we should consider before buying a new house.
rights and wrongs = all the good points and bad points of a situation （事情的真相、全部）
Regardless of the rights and wrongs of company policy, you need to give a month's notice.
tried and tested = something which has been well tested （经过反复考验的）
Using salt is a tried and tested way of getting red wine out of a carpet.
ups and downs = good and bad periods following one another in turn（盛衰，沉浮）
They have a lot of ups and downs in their relationship.
back and forth = not to stay still, but to keep traveling between two places （来回地，反复地）
I'm so glad I'm moving. I was getting sick of going back and forth every day. Now my fourney to work will be a lot quicker.
dribs and drabs = small unimportant amounts （点滴、少量）
The marathon runners finished in dribs and drabs.
said and done = to have the final word on something （说到底，毕竟）
When it's all said and done, the new reception area is going to be a credit to the company.
cat and mouse = doing something in the same way that a cat plays with a mouse （猫鼠游戏，欲擒故纵）
The guerillas played a cat and mouse game with the much better-equipped army.
trial and error = to do something new by making experiments and occasionally falling 反复试验
The new computer system has been installed. But it's a bit trial and error at the moment - nobody really knows how to use it.
flesh and blood = your family 家人
I have to help him if I can - he's my flesh and blood.
down and out = someone who has no money at all who has to live on the street （贫困的，贫病交迫的）
There are too many young down and outs in London.
by and large = generally （大体上，总的说来，一般的说）
By and large, our customers prefer good service to low prices.
bring and buy = a fair where people try to raise money for a cause by bringing something that other people might want to buy （慈善救济性自由集市）
I'm making a cake for the school's bring and buy next week.
hide and seek = a children's game where one child hides and the others try to find him / her （捉迷藏）
Someone's been playing hide and seek with the TV remote control again.
to and fro = another way of saying " back and forth " （往返地，来回地）
I'm exhausted - I've been going to and fro all week!
over and out = something you say to show you have come to the end of your message （通话完毕）
The last thing they heard from the pilot was 'over and out'.
done and dusted = properly finished （完毕，了结）
Well, that's this project done and dusted. We need a holiday now.
wine and dine = to entertain someone lavishly （以好酒好菜款待客人）
He's well-known for winning and dining his business partners.
bread and butter = your main source of income, or the most important issue （维持生活所需的）
Health and education are the bread and butter issues facing the UK government.
spick and span = ( of a room, house, etc.) completely clean and tidy again （房间、屋子等打扫得干干净净的；整洁的）
Her house is spick and span at all times
wheel and deal = to make deals in a skillful and perhaps dishonest way when buying and selling things （讨价还价，玩弄手段，投机取巧）
If you need a new car, try speaking to John. He's a bit of a wheeler and dealer.

注：这里的‘don'ts’和“nots”很少用，可以理解为复数形式！

如需转载请注明出处！

架构原理

Apache通常是开源界的首选Web服务器，因为它的强大和可靠，已经具有了品牌效应，可以适用于绝大部分的应用场合。但是它的强大有时候却显得笨重，配置文件得让人望而生畏，高并发情况下效率不太高。而轻量级的Web服务器Lighttpd却是后起之秀，其静态文件的响应能力远高于Apache，据说是Apache的2-3倍。Lighttpd的高性能和易用性，足以打动我们，在它能够胜任的领域，尽量用它。Lighttpd对PHP的支持也很好，还可以通过Fastcgi方式支持其他的语言，比如Python。

毕竟Lighttpd是轻量级的服务器，功能上不能跟Apache比，某些应用无法胜任。比如Lighttpd还不支持缓存，而现在的绝大部分站点都是用程序生成动态内容，没有缓存的话即使程序的效率再高也很难满足大访问量的需求，而且让程序不停的去做同一件事情也实在没有意义。首先，Web程序是需要做缓存处理的，即把反复使用的数据做缓存。即使这样也还不够，单单是启动Web处理程序的代价就不少，缓存最后生成的静态页面是必不可少的。而做这个是 Squid的强项，它本是做代理的，支持高效的缓存，可以用来给站点做反向代理加速。把Squid放在Apache或者Lighttpd的前端来缓存 Web服务器生成的动态内容，而Web应用程序只需要适当地设置页面实效时间即可。

即使是大部分内容动态生成的网站，仍免不了会有一些静态元素，比如图片、JS脚本、CSS等等，将Squid放在Apache或者Lighttp前端后，反而会使性能下降，毕竟处理HTTP请求是Web服务器的强项。而且已经存在于文件系统中的静态内容再在Squid中缓存一下，浪费内存和硬盘空间。因此可以考虑将Lighttpd再放在Squid的前面，构成 Lighttpd+Squid+Apache的一条处理链，Lighttpd在最前面，专门用来处理静态内容的请求，把动态内容请求通过proxy模块转发给Squid，如果Squid中有该请求的内容且没有过期，则直接返回给Lighttpd。新请求或者过期的页面请求交由Apache中Web程序来处理。经过Lighttpd和Squid的两级过滤，Apache需要处理的请求将大大减少，减少了Web应用程序的压力。同时这样的构架，便于把不同的处理分散到多台计算机上进行，由Lighttpd在前面统一把关。

在这种架构下，每一级都是可以进行单独优化的，比如Lighttpd可以采用异步IO方式，Squid可以启用内存来缓存，Apache可以启用MPM 等，并且每一级都可以使用多台机器来均衡负载，伸缩性很好。

实例讲解

下面以daviesliu.net和rainbud.net域下面的几个站点为例来介绍一下此方案的具体做法。daviesliu.net域下有几个用 mod_python实现的blog站点，几个php的站点，一个mod_python的小程序，以后可能还会架设几个PHP和Django的站点。而服务器非常弱，CPU为Celeron 500，内存为PC 100 384M，因此比较关注Web服务器的效率。这几个站点都是采用虚拟主机方式，开在同一台机器的同一个端口上。

Lighttpd服务于80端口，Squid运行在3128端口，Apache运行在81端口。

Lighttpd的配置

多个域名采用/var/www/domain/subdomain 的目录结构，用evhost模块配置document-root如下：

evhost.path-pattern        =  var.basedir + "/%0/%3/" 

FtpSearch中有Perl脚本，需要启用CGI支持，它是用来做ftp站内搜索的，缓存的意义不大，直接由lighttpd的mod_cgi处理：

$HTTP["url"] =~ "^/cgi-bin/" { # only allow cgi's in this directory
    dir-listing.activate = "disable"    # disable directory listings
    cgi.assign = ( ".pl"   =>  "/usr/bin/perl", ".cgi"  =>  "/usr/bin/perl" )
}

bbs使用的是phpBB，访问量不大，可以放在lighttpd(fastcgi)或者apache(mod_php)下，暂时使用 lighttpd，设置所有.php的页面请求有fastcgi处理：

fastcgi.server = ( ".php" =>  ( (  "host"  => "127.0.0.1", "port"=> 1026,  "bin-path"  =>  "/usr/bin/php-cgi"  )  ) )

blog.daviesliu.net 和 blog.rainbud.net 是用mod_python编写的blogxp程序，所有静态内容都有扩展名，而动态内容没有扩展名。blogxp是用python程序生成XML格式的数据再交由mod_xslt转换成HTML页面，只能放在Apache下运行。该站点采用典型Lighttpd+Squid+Apache方式处理：

$HTTP["host"] =~ "^blog" { 
    $HTTP["url"] !~ "\." {      
        proxy.server = ( "" => ( "localhost" => ( "host"=> "127.0.0.1", "port"=> 3128 ) ) )  #3128端口为
    }
}

share中有静态页面，也有用mod_python处理的请求，在/cgi/下：

$HTTP["host"] =~ "^share" {
    proxy.server = (
        "/cgi" => ( "localhost" => ( "host"=> "127.0.0.1", "port"=> 3128 )  )  
    )
}

Squid的配置

只允许本地访问：

http_port   3128
http_access allow localhost
http_access deny all

启用反向代理：

 httpd_accel_host 127.0.0.1
 httpd_accel_port 81                   #apache的端口
 httpd_accel_single_host on
 httpd_accel_with_proxy on          #启用缓存
 httpd_accel_uses_host_header on #启用虚拟主机支持

此方向代理支持该主机上的所有域名。

Apache的配置

配置/etc/conf.d/apache2，让其加载mod_python、mod_xslt、mod_php模块：

APACHE2_OPTS="-D PYTHON -D XSLT -D PHP5"

所有网站的根目录：

<Directory "/var/www">
   AllowOverride All     #允许.htaccess覆盖
    Order allow,deny
    Allow from all
</Directory>

基于域名的虚拟主机：

<VirtualHost *:81>
ServerName blog.daviesliu.net
DocumentRoot /var/www/daviesliu.net/blog
</VirtualHost>

这里明显没有lighttpd的evhost配置方便。

blog.daviesliu.net下的.htaccess设置(便于开发，不用重启Apache):

SetHandler mod_python
PythonHandler blogxp.publisher
PythonDebug On
PythonAutoReload On

<FilesMatch "\.">
    SetHandler None        #静态文件直接由Apache处理
</FilesMatch>

<IfModule mod_xslt.c>
    AddType text/xsl .xsl  #防止对xsl文件进行转化
    AddOutputFilterByType mod_xslt text/xml
    XSLTCache off
    XSLTProcess on
</IfModule>
Header set Pragma "cache"
Header set Cache-Control "cache"

在blogxp.publisher里面，还需要设置返回的文档类型和过期时间：

    req.content_type = "text/xml"
    req.headers_out['Expires'] = formatdate( time.time() + 60 * 5 )

经过这样的配置，所有站点都可以通过80、3128、81三个端口进行正常访问，80端口用作对外的访问，以减少负荷。81端口可以用作开发时的调试，没有缓存的困扰。

性能测试

由于时间和精力有限，下面只用ab2做一个并不规范的性能对比测试(每项都测多次取平均)，评价指标为每秒钟的请求数。
测试命令,以测试lighttpd上并发10个请求 scripts/prototype.js 为例：

ab2 -n 1000 -c 10 http://blog.daviesliu.net:80/scripts/prototype.js

静态内容：prototype.js (27kB)

在动态内容上，Squid的作用非常明显，而Lighttpd受限于Squid的效率，并且还要低一大截。如果是有多台Squid来做均衡的话，Lighttpd的功效才能发挥出来。
在单机且静态内容很少的情况下，可以不用Lighttpd而将Squid置于最前面。