How to use caching mechanism in PHP?

With the development of web applications, caching mechanism has become an important part of web development. By using caching mechanisms, the performance and response time of your application can be significantly improved. In PHP, the caching mechanism can be used to cache database query results, API responses, web page fragments, etc. This article will introduce how to use caching mechanism in PHP to improve application performance.

1. Why you need to use caching

In web applications, frequent queries and operations on the database are often required. For example, a shopping website may perform various operations on product inventory, order data, user information, etc. These operations will involve interaction with the database. However, performing database queries for every request will waste a lot of time and resources.

Because of this, we need to cache these results so that the data can be obtained faster on the next request without having to re-query the database. The caching mechanism can effectively reduce the burden on the server and reduce the response time and resource consumption of database operations.

2. The working principle of the caching mechanism

The caching mechanism mainly stores the requested results in the memory or hard disk, so that the next request can directly obtain the results from the cache without re-querying. . Caching mechanisms can generally be divided into two types: memory cache and hard disk cache.

Memory cache: A caching mechanism that stores data in memory, which can quickly obtain data. However, the cached data cannot exceed the capacity of the server's memory, otherwise it will cause the risk of memory leaks.

Hard disk cache: A caching mechanism that saves data in the hard disk. It can accommodate a large amount of data, but the speed of obtaining data is slower than the memory cache.

No matter which caching mechanism is used, the cache expiration time needs to be considered. If the validity period of cached data has expired, the data needs to be requeried and cached again.

3. How to use the caching mechanism

In PHP, the caching mechanism can be implemented by using the cache library. Common cache libraries include: Memcached, Redis and APC.

1. Memcached

Memcached is a high-performance memory caching system that can quickly access any type of data and is usually used to cache database query results. To use the Memcached library, you need to install and configure the Memcached service first.

Install Memcached service: sudo apt-get install memcached

Install Memcached library: sudo apt-get install php-memcached

Usage example:

$memcached = new Memcached();
$memcached->addServer('localhost', 11211); //连接Memcached服务

$key = 'data_key'; //缓存数据的键名
$data = $memcached->get($key); //尝试从缓存中获取数据

if (!$data) {  //如果缓存数据不存在，则去数据库获取数据并缓存结果
  $data = getDataFromDatabase();
  $memcached->set($key, $data, 60); //将数据缓存60秒
}

//使用$data数据

2. Redis

Redis is an open source cache and storage system that supports multiple data structures and cache types. Unlike Memcached, Redis can store cached data in memory or on the hard disk. Compared with Memcached, Redis supports more data types, such as Hash, String, List, etc., and can also be used as a persistent cache.

Install Redis service: sudo apt-get install redis-server

Install Redis library: sudo apt-get install php-redis

Usage example:

$redis = new Redis();
$redis->connect('localhost', 6379); //连接Redis服务

$key = 'data_key'; //缓存数据的键名
$data = $redis->get($key); //尝试从缓存中获取数据

if (!$data) {  //如果缓存数据不存在，则去数据库获取数据并缓存结果
  $data = getDataFromDatabase();
  $redis->set($key, $data, 60); //将数据缓存60秒
}

//使用$data数据

3. APC

APC (Alternative PHP Cache) is a lightweight PHP caching mechanism that can cache PHP script files, database query results and any data type. Compared with Memcached and Redis, APC cache data is stored in memory, but it should be noted that APC can only be used in a single server environment.

Install APC library: sudo apt-get install php-apc

Usage example:

//检查缓存是否存在
if (apc_exists('data_key')) {
  $data = apc_fetch('data_key'); //从缓存中获取数据
} else {
  $data = getDataFromDatabase();
  apc_store('data_key', $data, 60); //将数据缓存60秒
}

//使用$data数据

4. Best practices of caching mechanism

1. Choose the appropriate cache library

You need to decide which cache library to use based on project requirements and server resources. If you need to quickly obtain cached data, you can choose to use a memory cache library, such as Memcached and Redis. If you need to save a large amount of cached data, you can choose to use a hard disk cache library, such as Redis or APC.

2. Set a reasonable cache time

The cache time needs to be set according to the specific application conditions. If the data changes frequently, the cache time should be set shorter; if the data changes infrequently, the cache time can be set longer. At the same time, in order to avoid inconsistencies between cached data and actual data, the cached data can be updated before the cached data expires.

3. Avoid cache penetration and cache avalanche

Cache penetration refers to requesting a key that does not exist at all, so every request will go to the database to query, which will cause Server resources are wasted. The way to avoid cache penetration is to set default values ​​for keys that do not exist in the cache, such as empty strings or empty arrays.

Cache avalanche means that a large amount of cached data expires and is re-cached at the same time, causing excessive request pressure on the database and possibly causing server downtime. The way to avoid cache avalanches is to set different expiration times to prevent cached data from expiring at the same time.

4. Summary

The caching mechanism is an effective method to improve the performance and response time of web applications. In PHP, caching libraries such as Memcached, Redis and APC can be used to implement the caching mechanism. In order to ensure the effectiveness of the cache mechanism, it is necessary to select an appropriate cache library, set a reasonable cache time, and avoid cache penetration and cache avalanche. Through reasonable use of caching mechanisms, the performance and user experience of web applications can be improved.

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