I want to understand the various caches of PHP, please give me some advice.

I want to fix the cache, so I beg passersby to comment more
1. Full page static caching
That is to say, all pages are generated into html static pages. The static pages are directly accessed when users visit, without going through the PHP server parsing process. This method is more common in CMS systems, such as dedecms;

One of the more common implementation methods is to use output caching:

Ob_start()
******Code to run************
$content = Ob_get_contents();
****Write cached content to html file*****
Ob_end_clean();
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 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 product pages in shopping 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 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, they will 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 and the like;

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. When the same query is encountered next time, the data will be directly transferred from this file without going back. Check the database; but the cache file name here may need to be based on the query statement to establish a unique identifier;

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 time for cached files. Within this valid time, the same access will First retrieve the contents of the cache file, but if the set cache time is exceeded, you need to re-obtain the data from the database and produce the latest cache file; 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 is 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;

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 is actually accessing a static page and does not 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. Memory cache
When mentioning this, the first thing that may come to everyone's mind is Memcached; memcached is a high-performance distributed memory cache server. The general purpose of use is to reduce the number of database accesses by caching database query results to increase the speed and scalability of dynamic web applications.

It caches the information that needs to be cached into the system memory. When the information needs to be obtained, it is fetched directly from the memory; the more commonly used method is the key–>value method;

$memcachehost = '192.168.6.191';
$memcacheport = 11211;
$memcachelife = 60;
$memcache = new Memcache;
$memcache->connect($memcachehost,$memcacheport) or die ("Could not connect");
$memcache->set('key','cache content');
$get = $memcache->get($key); //Get information
?>
7. apache cache module
After apache is installed, it is not allowed to be cached. If an external cache or squid server requires web acceleration, it needs to be set in httpd.conf. Of course, the premise is that the mod_cache module must be activated when installing apache.

When installing apache: ./configure –enable-cache –enable-disk-cache –enable-mem-cache

8.php APC cache extension
Php has an APC cache extension, which is php_apc.dll under Windows. You need to load this module first, and then configure it in php.ini:

[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; Maximum time (seconds) for each PHP page to run, default 30 seconds
max_input_time = 600; The maximum time required for each PHP page to receive data, default 60
memory_limit = 128M; The maximum memory consumed by each PHP page, the default is 8M
9. Opcode cache
We know that the execution process of php can be shown in the following figure:
Image description
First, the PHP code is parsed into Tokens, then compiled into Opcode code, and finally the Opcode code is executed and the result is returned; therefore, for the same PHP file, its Opcode code can be cached the first time it is run, and the next time the page is executed, It will directly find the opcode code in the cache and execute the last step directly, without the need for intermediate steps.