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怎样提高php运行速度?

使用PHP的最大1个优势就是速度快。一般情况下,PHP总是具有足够的速度支持Web内容动态生成,许多时候甚至无法找出比它更快的方法。然而,当面对庞大的访问量、高负荷的应用、有限的带宽,以及其他各种带来性能瓶颈的因素时,就需要考虑怎样提高PHP的性能了。
1、代码优化
代码优化不仅仅是写出干净和清晰的代码,而是对代码进行一定的简化。可以使用Zend Optimizer来自动帮助完成这些繁杂的工作。Zend Optimizer可以从Zend Technologies的网站http://www.zend.com/免费得到,但必须同意它的许可约定,因为它不是以GPL方式发行的。它的原理很简单,即通过检测Zend引擎产生的中间代码,并对它进行优化,从而获得更高的执行速度。
在使用了Zend Optimizer后,复杂的PHP源程序的执行效率马上会得到显著提高,缺点是优化后的代码可读性下降,给代码修改带来困难。
Zend Optimizer的安装方法非常简单,只要根据用户使用的平台,下载相关的预编译版本,把下面2行代码加入到php.ini文件中,重新启动Web 服务器就行了:
zend_optimizer.optimization_level=15
zend_extension=″/path/to/ZendOptimizer.so″
zend_loader.enable=Off
额外增加的第三行代码是可选的,因为禁用zend_loader将会使优化速度更快。需要注意的是,只有在不使用Zend Encoder Runtime的时候,才可以禁用zend_loader。
2、使用缓存
如果PHP程序的规模很大,那么提高速度的办法就是使用缓存。现在已经有许多缓存方案可供选择,其中包括Zend Cache、APC和Afterburner Cache。
上面这几种都是“缓存模块”(caching modules)。第一次调用PHP文件时,缓存模块从PHP源代码生成一些中间代码,并把这些中间代码存储在Web服务器的内存中。以后再调用这些文件时,就可以直接使用内存中“编译”过的代码。这种方法确实能够改善应用的性能,因为它使得磁盘访问量减低到了最少的程度(代码已经读取和解析),代码直接在内存中运行,使得服务器响应请求的速度大大提高。
当然,缓存模块还会监视PHP源文件的变化,必要时会重新缓存页面,从而防止用户得到的页面仍旧由过时的PHP代码生成。由于缓存模块能够明显地降低服务器的负载,提高PHP应用的响应效率,因此它们非常适合于负载较大的网站使用。
Zend Cache是Zend Technologies公司开发的商业软件。在第一次运行后,PHP页面的运行速度立刻会有很大的提高,服务器的空闲资源也更多了。缺点是它不是免费的,但性价比还是很高的。
Afterburner Cache是Bware Technologies公司开发的免费缓存模块。功能与Zend Cache基本一样,但提高性能方面比不上Zend Cache。
APC(Alternative PHP Cache)是由Community Connect公司开发的另一种免费缓存模块,目前版本是2.0.4,可以从http://pecl.php.net/package/APC获得。对于产品应用来说,它的性能很稳定,而且也能在很大程度上提高响应请求的速度。
3、压缩网页内容
影响站点的访问速度还有1个重要因素,那就是下载速度。解决的办法就是压缩网页内容。对于纯文本内容而言,HTTP压缩技术可压缩至原大小的40%以下,从而提供60%以上的数据传输节约。虽然Web服务器会因为压缩导致CPU占用的略微上升,但可以节约大量用于传输的网络IO。
根据IETF规范,大部分浏览器都支持使用gzip压缩算法进行内容压缩。也就是说,可以先用gzip压缩网页内容,然后发送到客户端浏览器,浏览器在接收的时候会自动解压数据,再显示页面。这个过程对用户来说,是完全透明的。同样,压缩Web页面的内容也有不同的方法。
Mod_gzip是1种开放源代码的、标准的Apache模块,也叫互联网内容加速模块。可以将它和Apache一起编译,也可以作为DSO使用。相对于普通的浏览过程,它可以节省40%左右的流量。Mod_gzip不仅可以压缩静态的内容,如HTML、XML,而且对动态生成的,包括SQL、Java、WML、VRML等产生的内容,在服务器端进行实时压缩并传输,其压缩效率惊人,一般都为60%~85%。
压缩动态网页的内容,还可以使用class.gzip来对.php文件编码,class.gzip通过在PHP脚本的开头和结尾调用它的一些函数来压缩网页内容。如果整个站点都需要这样的压缩,可以在php.ini文件中的auto_prepend和auto_append中调用这些函数,但是会占用一定的系统开销。
PHP4.0.4推出了1种新的输出缓冲的处理手段—ob_gzhandler,它的作用和class.gzip完全一样,区别是可以直接把它加到php.ini 文件中,语法如下:
output_handler = ob_gzhandler;
这样将激活PHP的输出缓冲功能,并在发送内容前进行压缩。如果不想在这里设置,只在需要的地方才改变这个默认设置(不压缩),只要在需要压缩的PHP源程序目录中,修改一下.htaccess文件就行了,语法如下:
php_value output_handler ob_gzhandler
或者直接在PHP代码中调用它:
ob_start("ob_gzhandler");
输出缓冲的效果确实很理想,并且不会为服务器带来额外的系统开销。要注意的一点是Netscape Communicator不支持图像的压缩。因此除非知道访问者都使用Internet Explorer,否则必须禁止压缩jpeg和gif图象。
4 其它技巧
在编程时,使用一些小技巧也可以加快PHP的运行速度:
(1)用i+=1代替i=i+1,既符合c/c++的习惯,效率相对还更高。
(2)尽可能使用PHP内部函数。
(3)能使用单引号字符串时,尽量使用单引号字符串。单引号字符串的效率要高于双引号字符串。
(4)用foreach代替while遍历数组,foreach的效率明显高于while循环,而且不需要调用reset函数。

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