Caching in PHP

With the rapid development of the Internet, the number of visits to websites and applications has also increased exponentially. In order to meet the needs of users, developers have implemented various techniques to improve the performance of websites and applications. One of the important technologies is caching.

Caching refers to storing frequently accessed data or calculation results in high-speed storage devices so that they can be obtained and used faster. Caching technology can significantly improve application response times, reduce server load and reduce data transfer costs. As a popular web development language, PHP also provides some caching technologies to optimize the performance of web applications.

The cache in PHP is divided into two categories: memory cache and file cache. These two types of caches will be introduced below.

1. Memory caching

Memory caching is caching data in memory for faster access. There are many memory cache extensions in PHP, such as APC, Memcached and Redis.

APC (Alternative PHP Cache) is an open source PHP extension that can cache compiled PHP code in memory. This avoids the need to recompile the PHP code for each request and improves the response speed of the page. In addition, APC also provides a user cache where developers can store any data that needs to be cached. Using APC can significantly reduce server load and improve application performance.

Memcached is a distributed memory object caching system that can be used to store any type of data. It stores data in memory and provides a distributed cache server cluster so that data can be shared among different servers. Developers can use it to cache database query results, page content, session data, etc. Since the data is stored in memory, access is very fast. Therefore, it is widely used in large-scale web applications.

Redis is also an in-memory cache system, but it is more flexible and can store various types of data structures, such as strings, hashes, lists, sets, and ordered sets. Redis also provides some advanced features, such as publish/subscribe, transactions, Lua scripts, and distributed locks. Compared to Memcached, Redis has higher performance and can be used for applications that require more complex data structures.

2. File caching

File caching is to cache data into a file on the hard disk so that the data can be read from the file on the next request without the need to calculate it again. Or retrieve from database. PHP also provides some file caching technologies, such as APC, XCache and Zend Opcache.

Both APC and XCache can cache data into files. These files are usually stored in temporary directories. When data is modified, the file is updated. When this data needs to be accessed, PHP will check whether the file exists and read the data from the file if it exists, otherwise it will recalculate or read the data from the database. Because file caching requires access to the hard disk, it is slower than memory caching, but it can still significantly improve application performance.

Zend Opcache is a built-in extension in PHP 5.5 and later versions, which provides bytecode caching functionality. When PHP files are executed, they are first compiled into bytecode before they can be executed. Zend Opcache can cache these bytecodes in memory for faster loading and execution. This can significantly improve the responsiveness of the page.

Summary

Caching technology is key to optimizing web application performance. In PHP, developers can use memory cache and file cache to implement caching functions. Extensions such as APC, Memcached, Redis, XCache and Zend Opcache provide rich caching solutions for PHP. By using these tools, developers can easily implement caching and improve application performance.

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