Summary of 9 major caching technologies in PHP_PHP Tutorial-PHP Tutorial-php.cn

A summary of the 9 major caching technologies in PHP

1. Full page static caching

That is to say, all pages are generated as html static pages. The static pages are directly accessed when users visit, without going through the process of PHP server parsing. This method is more common in CMS systems, such as dedecms;

A common implementation method is to use output caching:

<code><span class="typ">Ob_start<span class="pun">()<span class="pln">
<span class="pun">******要运行的代码*******<span class="pln">
$content <span class="pun">=<span class="pln"> <span class="typ">Ob_get_contents<span class="pun">();<span class="pln">
<span class="pun">****将缓存内容写入<span class="pln">html<span class="pun">文件*****<span class="pln">
<span class="typ">Ob_end_clean<span class="pun">();</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>

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2. Partial cache of the page

This method is to statically cache the infrequently changing parts of a page, while frequently changing blocks are not cached, and are finally assembled together for display; this can be achieved using a method similar to ob_get_contents, or using a method similar to ESI The page fragment caching strategy of this class is used to cache relatively static fragment parts in dynamic pages (ESI technology, please Baidu, not detailed here).

This method can be used for example, on product pages in malls;

3. Data caching

As the name suggests, it is a way of caching data; for example, when a certain product information in the mall is requested using the product ID, data including store information, product information, etc. can be obtained. At this time, these can be The data is cached in a PHP file, and the file name contains the product ID to create a unique identifier; the next time someone wants to view this product, they will first directly adjust the information in this file without querying the database; in fact, the cache file is cached is just a php array;

This method is used in the Ecmall mall system;

4. Query cache

In fact, this is the same idea as data caching, which is to cache according to the query statement; cache the data obtained by the query in a file. The next time the same query is encountered, the data will be directly transferred from this file first. I will check the database again; but the cache file name here may need to be uniquely identified based on the query statement;

Caching based on time changes

Actually, this is not a real caching method; the caching technologies 2, 3, and 4 above generally use time change judgment; that is, you need to set a valid time for cached files. Within this valid time, the same The content of the cache file will be fetched first when accessing, but if the set cache time is exceeded, the data needs to be re-obtained from the database and the latest cache file will be generated; for example, I set the homepage of our mall to be updated every 2 hours;

5. Cache according to content changes

This is not an independent caching technology and needs to be used in combination; that is, when the database content is modified, the cache file will be updated immediately;
For example, in a mall with a lot of traffic and a lot of products, the product table must be relatively large, and the pressure on this table is also heavy; we can page cache the product display page;

当商家在后台修改这个商品的信息时，点击保存，我们同时就更新缓存文件；那么，买家访问这个商品信息时，实际上访问的是一个静态页面，而不需要再去访问数据库；

试想，如果对商品页不缓存，那么每次访问一个商品就要去数据库查一次，如果有10万人在线浏览商品，那服务器压力就大了；

6、内存式缓存

提到这个，可能大家想到的首先就是Memcached；memcached是高性能的分布式内存缓存服务器。一般的使用目的是，通过缓存数据库查询结果，减少数据库访问次数，以提高动态Web应用的速度、提高可扩展性。

它就是将需要缓存的信息，缓存到系统内存中，需要获取信息时，直接到内存中取；比较常用的方式就是 key–>value方式；

<code><span class="pun"><?<span class="pln">php 
     $memcachehost <span class="pun">=<span class="pln"> <span class="str">&#39;192.168.6.191&#39;<span class="pun">;<span class="pln">
     $memcacheport <span class="pun">=<span class="pln"> <span class="lit">11211<span class="pun">;<span class="pln">
     $memcachelife <span class="pun">=<span class="pln"> <span class="lit">60<span class="pun">;<span class="pln">
     $memcache <span class="pun">=<span class="pln"> <span class="kwd">new<span class="pln"> <span class="typ">Memcache<span class="pun">;<span class="pln">
     $memcache<span class="pun">-><span class="pln">connect<span class="pun">(<span class="pln">$memcachehost<span class="pun">,<span class="pln">$memcacheport<span class="pun">)<span class="pln"> <span class="kwd">or<span class="pln"> <span class="kwd">die<span class="pln"> <span class="pun">(<span class="str">"Could not connect"<span class="pun">);<span class="pln">
     $memcache<span class="pun">-><span class="kwd">set<span class="pun">(<span class="str">&#39;key&#39;<span class="pun">,<span class="str">&#39;缓存的内容&#39;<span class="pun">);<span class="pln">
     $get <span class="pun">=<span class="pln"> $memcache<span class="pun">-><span class="kwd">get<span class="pun">(<span class="pln">$key<span class="pun">);<span class="pln">       <span class="com">//获取信息<span class="pln">
<span class="pun">?></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>

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7、apache缓存模块

apache安装完以后，是不允许被cache的。如果外接了cache或squid服务器要求进行web加速的话，就需要在htttpd.conf里进行设置，当然前提是在安装apache的时候要激活mod_cache的模块。

安装apache时：./configure –enable-cache –enable-disk-cache –enable-mem-cache

8、php APC缓存扩展

Php有一个APC缓存扩展，windows下面为php_apc.dll，需要先加载这个模块，然后是在php.ini里面进行配置：

<code><span class="pun">[<span class="pln">apc<span class="pun">]<span class="pln"> 
     extension<span class="pun">=<span class="pln">php_apc<span class="pun">.<span class="pln">dll 
     apc<span class="pun">.<span class="pln">rfc1867 <span class="pun">=<span class="pln"> on 
     upload_max_filesize <span class="pun">=<span class="pln"> <span class="lit">100M<span class="pln"> 
     post_max_size <span class="pun">=<span class="pln"> <span class="lit">100M<span class="pln"> 
     apc<span class="pun">.<span class="pln">max_file_size <span class="pun">=<span class="pln"> <span class="lit">200M<span class="pln"> 
     upload_max_filesize <span class="pun">=<span class="pln"> <span class="lit">1000M<span class="pln"> 
     post_max_size <span class="pun">=<span class="pln"> <span class="lit">1000M<span class="pln"> 
     max_execution_time <span class="pun">=<span class="pln"> <span class="lit">600<span class="pln"> <span class="pun">;<span class="pln">   <span class="pun">每个<span class="pln">PHP<span class="pun">页面运行的最大时间值(秒)，默认<span class="lit">30<span class="pun">秒<span class="pln"> 
     max_input_time <span class="pun">=<span class="pln"> <span class="lit">600<span class="pln"> <span class="pun">;<span class="pln">       <span class="pun">每个<span class="pln">PHP<span class="pun">页面接收数据所需的最大时间，默认<span class="lit">60<span class="pln"> 
     memory_limit <span class="pun">=<span class="pln"> <span class="lit">128M<span class="pln"> <span class="pun">;<span class="pln">       <span class="pun">每个<span class="pln">PHP<span class="pun">页面所吃掉的最大内存，默认<span class="lit">8M</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>

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9、Opcode缓存

我们知道，php的执行流程可以用下图来展示：
Summary of 9 major caching technologies in PHP_PHP Tutorial
首先php代码被解析为Tokens，然后再编译为Opcode码，最后执行Opcode码，返回结果；所以，对于相同的php文件，第一次运行时可以缓存其Opcode码，下次再执行这个页面时，直接会去找到缓存下的opcode码，直接执行最后一步，而不再需要中间的步骤了。

比较知名的是XCache、Turck MM Cache、PHP Accelerator等。