Introduction to php caching technology_PHP tutorial-PHP Tutorial-php.cn

Cache refers to the temporary file exchange area. The computer pulls the most commonly used files from the memory and temporarily places them in the cache, just like moving tools and materials to the workbench. This is more convenient than going to the warehouse to retrieve them when they are used. Because the cache often uses RAM (non-permanent storage that is lost when the power is turned off), the files will still be sent to the hard disk and other storage for permanent storage after the work is completed. The largest cache in a computer is the memory stick. The fastest ones are the L1 and L2 caches built into the CPU. The video memory of the graphics card is a cache for the GPU. There is also a 16M or 32M cache on the hard disk. Never understand cache as one thing, it is a general term for a processing method!

The most effective way to cope with high traffic in WEB development is to use caching technology, which can effectively improve server load performance and trade space for time.

The Internet is also a 2 8 conclusion. Just like the keywords in Baidu search, 80% of people are searching for 20% of the content, so you only need to save the content of these 20% of keywords If it is good, it can quickly return the content the user needs among billions of records very efficiently.

In this article, let’s take a look at some storage methods commonly used in PHP WEB development.

1. Universal caching technology:

Data caching: The data caching mentioned here refers to the database query PHP caching mechanism. Every time you access a page, it will first Detect whether the corresponding cached data exists. If it does not exist, connect to the database, obtain the data, and serialize the query results and save them to the file. In the future, the same query results will be obtained directly from the cache table or file.

The most widely used example is the search function of Discuz, which caches the result ID into a table and searches the cache table first when searching for the same keyword next time.

As a common method, when multiple tables are associated, the contents in the attached table are generated and saved into an array in a field of the main table. When needed, the array is decomposed. The advantage of this is that only one table can be read. , the disadvantage is that there will be many more steps to synchronize the two data. The database is always the bottleneck. Trading the hard disk for speed is the key point of this.

2. Page cache:

Every time you access a page, it will first check whether the corresponding cached page file exists. If it does not exist, connect to the database and get Data, display the page and generate a cache page file at the same time, so that the page file will be effective the next time you visit. (Template engines and some common PHP caching mechanism classes on the Internet usually have this function)

３. Time-triggered caching:

Check whether the file exists and the timestamp is less than the setting The expiration time, if the file modification timestamp is greater than the current timestamp minus the expiration timestamp, then use the cache, otherwise update the cache.

４. Content-triggered caching:

When data is inserted or updated, the PHP cache mechanism is forced to be updated.

５. Static cache:

The static cache mentioned here refers to static, directly generating text files such as HTML or XML, and regenerating them when there are updates. , suitable for pages that don’t change much, so I won’t talk about it here.

The above content is a code-level solution. I directly CP other frameworks and am too lazy to change. The content is similar, it is easy to do, and can be used in several ways, but the following The content is a server-side caching solution, not at the code level. It requires the cooperation of multiple parties to achieve

６. Memory cache:

Memcached is high-performance and distributed A memory-based object PHP caching mechanism system used to reduce database load and improve access speed in dynamic applications.

７. PHP buffer:

There are eaccelerator, apc, phpa, xcache, I won’t talk about this one, search a bunch of them yourself Look, it’s OK to know that this thing exists

８. MYSQL cache:

This is also considered non-code level. Classic databases use this method. Look at the running time below, 0.09xxx and the like

９. Web cache based on reverse proxy:

Such as Nginx, SQUID, mod_proxy (apache2 and above are divided into For mod_proxy and mod_cache)

10. DNS polling: 　

BIND is an open source DNS server software. This is a big deal to mention. Search it yourself Go ahead, just let everyone know that this thing exists.
I know that some large websites such as chinacache do this. To put it simply, it is multi-server. The same page or file is cached on different servers and automatically parsed to the relevant server according to the north and south.

Why use caching technology? The reason is simple: improve efficiency.In program development, the main way to obtain information is to query the database. In addition, it may also be through Web Services or some other method. No matter which method is used, they may become an efficiency bottleneck in the face of a large number of concurrent accesses. , in order to solve these problems, people have proposed many solutions, some of which use optimization software (such as: APC, Eaccelerator, Zend Optimizer, etc.) to improve the running efficiency of the program. Reasonable use of these software can often make the program run smoothly. The efficiency has been improved by orders of magnitude, but the premise is that you must have control of the host to be able to install these software. If you are using a virtual host, you can only pray that your service provider has pre-installed some optimization software. , otherwise you must use PHP yourself to implement the corresponding caching function. If this makes you feel at a loss, I believe the following text can give you some inspiration.

Many PHP programmers use golden partners like Adodb+Smarty, so let’s first take a look at how to use their caching function.

First take a look at the data caching function provided by adodb:

include('adodb.inc.php'); # load code common to ADOdb
$ ADODB_CACHE_DIR = '/usr/ADODB_cache';
$conn = &ADONewConnection('mysql'); # create a connection
$conn->PConnect('localhost','userid','','agora' );# connect to MySQL, agora db
$sql = 'select CustomerName, CustomerID from customers';
$rs = $conn->CacheExecute(15,$sql);
?>

As above, every time the data is queried, the corresponding results will be serialized and saved in the file. In the future, the same query statement can be obtained from the cache file without directly querying the database.

Let’s take a look at the page caching function provided by Smarty:

require('Smarty.class.php');
$smarty = new Smarty;

$smarty->caching = true;

if(!$smarty->is_cached('index.tpl')) {
// No cache available, do variable assignments here.
$contents = get_database_contents();
$smarty->assign($contents);
}

$smarty->display('index.tpl');
?>

As above, every time you access a page, it will first check whether the corresponding cache exists. If it does not exist, connect to the database, get the data, complete the assignment of template variables, and display the page. At the same time, a cache file is generated, so that the cache file will be used the next time it is accessed, and the data query statement of the if block will not be executed. Of course, there are many things to consider in actual use, such as the setting of the validity period, the setting of the cache group, etc. For details, you can check the relevant chapters on caching in the Smarty manual.

The above two popular PHP component caching methods have different focuses. For Adodb's cache, it caches data, while for Smarty's cache, it caches pages. There are many other components that provide caching functions (such as: PEAR::Cache_Lite, etc.). Which solution to use in actual programming requires specific analysis of the specific situation, and may also be used comprehensively.

An obvious benefit of using the built-in caching solutions of these components is that their implementation is transparent to the client. Just make the necessary settings (such as cache time, cache directory, etc.) without thinking too much about the details of caching. The system will automatically manage the cache according to the settings. But its shortcomings are also obvious, because each request still needs to be parsed by PHP, and the efficiency is still greatly reduced compared with pure static. It still cannot meet the requirements in the face of large PV. In this case, just doing dynamic caching is not enough. Yes, static caching must be implemented.