Detailed introduction to the summary of nine major caching technologies in PHP

1. Full page static caching

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

A more common implementation method is to use output caching:

Ob_start()******要运行的代码*******$content = Ob_get_contents();****将缓存内容写入html文件*****Ob_end_clean();

2. Page partial caching

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 pages such as ESI. The fragment caching strategy is used to cache relatively static fragment parts of 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, in a mall When a certain product information is requested using the product ID, data including store information, product information, etc. will be obtained. At this time, these data can be cached in a php file. The file name contains the product ID to create a unique identifier. ;The next time someone wants to view this product, first directly adjust the information in this file without querying the database; In fact, what is cached in the cache file is a php array or the like;

In the Ecmall mall system This method is used;

4. Query caching

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 you encounter the same query, you will directly retrieve the data from this file instead of checking the database; however, the cache file name here may need to be uniquely identified based on the query statement;

Caching based on time changes

In fact, 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 cache file time, within this valid time, the same access will first fetch the contents of the cache file. However, if the set cache time is exceeded, the data needs to be obtained from the database again and the latest cache file will be produced; for example, I will The homepage is set 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; it means that when the database content is modified, it will be updated immediately Cache files;
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 cache the product display page;

When the merchant modifies the product information in the background, click Save, and we will update the cache file at the same time; then, when the buyer accesses the product information, he actually accesses a static page without the need to access the database;

Just imagine, if the product page is not cached, then every time you access a product, you have to check the database. If 100,000 people browse the product online, the pressure on the server will be great;

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；

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

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：

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

9、Opcode缓存

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。

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