Detailed explanation of the application of caching technology in PHP_PHP Tutorial

PHP,一门最近几年兴起的web设计脚本语言,由于它的强大和可伸缩性,近几年来得到长足的发展,php相比传统的asp网站,在速度上有绝对的优势,想mssql转6万条数据php如需要40秒,asp不下2分钟.但是,由于网站的数据越来越多,我们渴求能更快速的调用数据,不必要每次都从数据库掉,我们可以从其他的地方,比方一个文件,或者某个内存地址,这就是php的缓存技术,也就是Cache技术.


一般来说,缓存的目的是把数据放在一个地方让访问的更快点,毫无疑问,内存是最快的,但是,几百M的数据能往内存放么?这不现实,当然,有的时候临时放如服务器缓存,如ob_start()这个缓存页面开启的话在发送文件头之前页面内容都被缓存在内存中,知道等页面输出自动清楚或者等待ob_get_contents的返回,[或者被ob_end_clean显示的清除,这在静态页面的生成中能很好的利用,在模板中能得到很好的体现,我的这篇文章深入的讨论了:

 谈PHP生成静态页面,这是一种方式,但这是临时性的,不是解决我们问题的好方法.

另外,在asp中有一对象application,可以保存公用的参数,这也算点缓存,但在php,我至今没看到开发者产出这种对象,的确,没必要.asp.net的页面缓存技术就用的是viewstate,而cache就是文件关联,(不一定准确),文件被修改,更新缓存,文件没被修改而且不超时(注释1),就读取缓存,返回结果,就是这个思路,看看这个源码:

class cache{
/*
Class Name: cache
Description: control to cache data,$cache_out_time is a array to save cache date time out.
Version: 1.0
Author: Old farmer cjjer
Last modification:2006-2-26
Author URL: http://www.cjjer.com
*/
private $cache_dir;
private $expireTime=180;//The cache time is 60 seconds
function __construct($cache_dirname){
if(!@is_dir($cache_dirname)){
if(!@mkdir($cache_dirname ,0777)){
                                                                                                                                                                                    ,,,,,,,,,,,;,; ;cache_dir = $cache_dirname;
}
function __destruct(){
echo Cache class bye.;
}

function get_url() {
if (!isset( $_SERVER[REQUEST_URI])) {
                                                                                                               🎜>                                                                                                            _SERVER[QUERY_STRING])) ? ? . $_SERVER[QUERY_STRING] : ;
}

return $url;
}

function warn($errorstring){
echo "An error occurred:

".$errorstring."

";
}

function cache_page($pageurl,$pagedata){
if(!$fso=fopen($pageurl,w)){
$this->warns(Cache file cannot be opened.);// trigger_error
return false;
}
if(!flock($fso,LOCK_EX)){//LOCK_NB, exclusive lock
$this->warns(Cache file cannot be locked.) ;//trigger_error
return false;
}
if(!fwrite($fso,$pagedata)){//Write byte stream, serialize to write other formats
$this-> ;warns(Unable to write to cache file.);//trigger_error
return false;
}
flock($fso,LOCK_UN);//Release lock
fclose($fso);
return true;
}

function display_cache($cacheFile){
if(!file_exists($cacheFile)){
$this->warn(Cache file cannot be read. );//trigger_error
return false;
}
echo Read cache file:.$cacheFile;
//return unserialize(file_get_contents($cacheFile));
$fso = fopen ($cacheFile, r);
$data = fread($fso, filesize($cacheFile));
fclose($fso);
return $data;
}

function readData($cacheFile=default_cache.txt){
$cacheFile = $this->cache_dir."/".$cacheFile;
if(file_exists($cacheFile)&&filemtime($cacheFile)>( time()-$this->expireTime)){
                                                                                     else{
                $data="from here wo can get it from mysql database,update time is ".date(l dS of F Y h:i:s A).", The expiration time is: ".date(l dS of F Y h:i:s A,time()+$this->expireTime)."----------";
$this ->cache_page($cacheFile,$data);
}
      return $data;
}



}
?>

Below I will interrupt this code to explain it line by line.
Three: Program Dialysis

This cache class (class is nothing good) Scared. Please continue reading) The name is cache and has 2 attributes:

private $cache_dir;
private $expireTime=180;

$cache_dir is the parent directory of the relative website directory where the cache file is placed, $expireTime(Comment One ) is the expiration time of our cached data, mainly based on this idea:
When the data or file is loaded, first determine whether the cache file exists, return false, and the file was last modified Is the sum of time and cache time greater than the current time? If it is greater, it means that the cache has not expired. If it is smaller, it returns false. When false is returned, the original data is read, written to the cache file, and the data is returned. ,

Then look at the program:

function __construct($cache_dirname){
if(!@is_dir($cache_dirname)){
if(!@mkdir($cache_dirname,0777)){
$this-> ;warn(The cache file does not exist and cannot be created, it needs to be created manually.); >
When the class is instantiated for the first time, a default function is constructed with parameters to cache the file name. If the file does not exist, create a folder with editing permissions. An exception will be thrown when the creation fails. Then $ of the cache class The cache_dir attribute is set to this folder name. All our cache files are in



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http: //www.bkjia.com/PHPjc/509203.htmlTechArticlePHP, a web design scripting language that has emerged in recent years, due to its power and scalability, has recently PHP has made great progress in the past few years. Compared with traditional ASP websites, PHP has an absolute advantage in speed. I think...