This tutorial quickly explains the PHP caching mechanism and its applications.

Efficient performance is the key to PHP application development. Facing thousands or even millions of users, the performance and availability of web applications face huge challenges. Caching technology can effectively avoid performance bottlenecks and improve application efficiency.

Core Points

• The cache stores frequently accessed data in a temporary location, reducing the number of times data is read from the original location, thereby improving PHP application performance.
• Output buffering is a technique in PHP that stores script output in a buffer before being displayed to the user, allowing modifications or other operations before being displayed.
• PHP provides a variety of cached data functions, such as apc_store(), memcache_set() and xcache_set(), which store data in memory and access much faster than data on hard drives.
• PHP cache can also use a database to store cached data, which is useful when cached large amounts of data or requires access to cached data from multiple servers.

What is cache?

Caching is a technique that stores frequently accessed data in a temporary storage location to reduce the number of times data is retrieved from the original storage location. This can greatly improve the performance of a website or application, because accessing data from a cache is often much faster than accessing data from its source.

PHP provides a variety of ways to implement caching. Let's take a look separately.

Output Buffer

Output buffering is a technique in PHP that allows us to store the output of PHP scripts in a buffer instead of sending it directly to the browser. This allows us to modify the output or perform other actions on the output before displaying it to the user.

To start the output buffering, we can use the ob_start() function. This function will turn on the output buffer and start capturing all output sent by the script. The output can then be stored in a variable using the ob_get_contents() function. Finally, you can end the output buffering using the ob_end_flush() function and send the output to the browser, or you can discard it using the ob_end_clean() function.

The following is an example of how to use output buffering:

<?php
ob_start(); // 開始輸出緩沖

echo '此輸出將存儲在緩沖區(qū)中';

$output = ob_get_contents(); // 獲取輸出緩沖區(qū)的內(nèi)容
ob_end_clean(); // 結(jié)束輸出緩沖區(qū)并丟棄內(nèi)容

echo '此輸出將發(fā)送到瀏覽器';
?>

In this example, only the string "This output will be sent to the browser" will be output because we discarded the contents of the output buffer containing the first echo instruction.

Output buffer can be used as a cache because it allows us to store the output of a PHP script in memory instead of regenerating it every time the script is accessed.

Cache function

PHP provides some functions specifically for caching data, including apc_store(), memcache_set() and xcache_set(). These functions can be used to store data in memory and access much faster than data stored on a hard drive.

apc_store()

apc_store() function is part of the Alternative PHP Cache (APC) extension that provides opcode cache for PHP. (Opcode caching is a PHP performance optimization technique that caches the compiled bytecode of PHP scripts into memory instead of reparsing and recompiling the source code every time it requests.) It uses specified keys and expired Time stores the value in the APC cache.

The following is an example of how to cache values ??into memory using the apc_store() function:

<?php
ob_start(); // 開始輸出緩沖

echo '此輸出將存儲在緩沖區(qū)中';

$output = ob_get_contents(); // 獲取輸出緩沖區(qū)的內(nèi)容
ob_end_clean(); // 結(jié)束輸出緩沖區(qū)并丟棄內(nèi)容

echo '此輸出將發(fā)送到瀏覽器';
?>

To retrieve the cached value, we can use the apc_fetch() function:

<?php
$value = '這是要緩存的值';

// 將值存儲在緩存中一小時
apc_store('cache_key', $value, 3600);
?>

For more information on apc_store(), see here. (Relevant links should be inserted here)

memcache_set()

memcache_set() function is part of the Memcache extension, which allows you to use the Memcache server as a cache for PHP. It stores the value in the Memcache server using the specified key and expiration time.

For more information on memcache_set(), see here. (Relevant links should be inserted here)

xcache_set()

xcache_set() function is part of the XCache extension, which provides PHP opcode cache and data cache. It stores the value in the XCache cache using the specified key and expiration time.

For more information on xcache_set(), see here. (Relevant links should be inserted here)

Cache with database

Another option to cache in PHP is to use a database to store cached data. This seems to contradict the main goal of cache (reducing database access and improving performance). However, in some cases, it can be useful to cache data in a database.

One case is that you need to cache large amounts of data that may not be suitable for memory. Additionally, if you need to access cached data from multiple servers, it can be useful to cache data in the database as it allows easy sharing of cached data between servers.

To cache data into a database, you can use a table with at least two columns: one for cache keys and the other for cache data. You can then use a SELECT query to check if the cache key exists in the table and use an INSERT or UPDATE query to store the data into the table.

The following is an example of how to cache data in a MySQL database:

<?php
$cachedValue = apc_fetch('cache_key');

if ($cachedValue) {
    // 使用緩存的值
    echo $cachedValue;
} else {
    // 生成值并將其存儲在緩存中
    $value = '這是要緩存的值';
    apc_store('cache_key', $value, 3600);
    echo $value;
}
?>

This example demonstrates how to check if the cache key exists in the cache table and, if so, how to update the cache value. If the cache key does not exist, a new row containing the cache key and value is inserted into the table. The cached value is then retrieved from the table and displayed to the user.

Conclusion

Cache is a very powerful technology that can improve the performance of PHP websites or applications. PHP provides a variety of options for implementing caching, including output buffering, cache functions, and using databases for caching. By storing frequently accessed data in a temporary location, we can reduce the number of times we retrieve data from its sources and improve the overall speed and performance of the site.

PHP Caching FAQs (FAQs)

What is PHP cache and why it matters?

PHP cache is a process of storing the output of PHP code in the cache so that future requests to the same data can be provided faster. This is important because it can significantly reduce server load and improve site performance. By storing the output of PHP code, the server does not have to repeatedly execute the same code for each user, saving time and resources.

How does PHP cache work?

PHP cache works by storing the output of the PHP script in the cache. When a user requests a page, the server first checks whether the cached version of the page exists. If present, the server will provide a cached version, thus eliminating the need to execute PHP scripts. If the cached version does not exist, the server executes the PHP script, generates the page and stores the output in the cache for future use.

What are the different types of PHP caches?

There are several types of PHP cache, including opcode cache, user data cache, and page cache. The opcode cache stores compiled PHP code, so the server does not have to compile the code every time it requests. User data cache stores the results of database queries or API calls, thus reducing the need for duplicate queries or calls. The page cache stores the entire HTML output of the page, allowing the server to serve the page without executing any PHP code.

How do I implement PHP cache in my application?

There are several ways to implement PHP cache in your application. One of the most commonly used methods is to use PHP cache extensions such as APC or OPcache. These extensions provide a way to easily implement opcode caching in your application. For user data cache, you can use cache systems such as Memcached or Redis. For page caching, you can use reverse proxy such as Varnish or PHP classes such as PHPFastCache.

What are the benefits of PHP caching?

PHP cache provides many benefits. It significantly improves website performance by reducing server load and response time. It can also reduce the need for duplicate database queries or API calls, saving resources and increasing efficiency. Additionally, it can help your website handle more traffic without the need for additional server resources.

Is there any disadvantage of PHP cache?

While PHP cache offers many benefits, it also has some potential drawbacks. One of the main drawbacks is that it may make debugging more difficult, as changes to PHP code may not be reflected immediately due to the cached version provided. Additionally, if improperly managed, caching may result in the provision of outdated content to the user.

How to clear PHP cache?

Clearing the PHP cache can be done in several ways, depending on the type of cache you are using. For opcode caching, you can clear the cache using the functions provided by the cache extension. For user data cache, you can use the methods provided by the cache system to clear the cache. For page caching, you can clear the cache by deleting the cache file or using methods provided by a cache class or reverse proxy.

How to optimize PHP cache?

Optimizing PHP cache includes fine-tuning your cache policy to ensure maximum performance. This may include adjusting the cache lifecycle, deciding which data is cached and which data is not cached, and using different types of caches for different parts of the application. Additionally, monitoring your cache usage and performance can help you identify areas of improvement.

Can I use PHP cache on a shared hosting?

Yes, you can use PHP cache on shared hosting. However, depending on your hosting provider, options may be limited. Some providers may not allow you to install PHP extensions or cache systems. In this case, you can use PHP classes that provide caching functionality without any extensions or systems.

What is the difference between client cache and server cache?

Client cache involves storing data on a user's device, while server-side cache involves storing data on a server. Both types of caches are designed to improve performance by reducing the need for duplicate requests or calculations. However, they are used in different scenarios and have different advantages and limitations. For example, server-side caching can reduce server load and increase response time, while client-side caching can reduce network latency and save bandwidth.

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