How to use Memcache for distributed caching in PHP development?

As web applications become increasingly complex, performance has become a critical issue. In many applications, database queries are one of the most time-consuming operations. In order to avoid frequently reading data from the database, a caching system can be used to store frequently read data in memory for quick access. In PHP development, using Memcached for distributed caching is an extremely common practice. In this article we will introduce how to use Memcached for distributed caching.

What is Memcached?

Memcached is a high-performance distributed memory caching system that can share cached data among multiple servers. More specifically, Memcached is a key-value cache system that stores data in memory. It allows developers to cache all types of data in their applications, including HTML pages, database query results, and even complete web applications.

Installing and Configuring Memcached

Before using Memcached, we need to install it first. On a Linux system, you can install it with the following command:

sudo apt-get install memcached
sudo apt-get install php-memcached

After the installation is complete, you need to start the Memcached service, which can be started with the following command:

sudo service memcached start

Next, we need to configure Memcached in PHP Extension modules. On Ubuntu systems, this can be configured by editing the following file:

sudo vi /etc/php/7.0/mods-available/memcached.ini

Add the following content to the file:

extension=memcached.so

Save and close the file, then restart the Apache server:

sudo service apache2 restart

Now, you have successfully installed and configured Memcached.

Using Memcached for distributed caching

Next, we will show how to use Memcached for distributed caching. First, we need to create a Memcached instance, you can use the following code:

$mc = new Memcached();
$mc->addServer("127.0.0.1", 11211); // 添加一个Memcached服务器

In the above code, we create a Memcached instance and add a Memcached server. The first parameter of the addServer() function is the IP address of the Memcached server, and the second parameter is the port number (default is 11211).

Next, let’s look at a specific example of caching database query results into Memcached. We assume that we have defined a function fetchUserById() that accepts a user ID as a parameter and returns the user's information. Here is the code to achieve this:

function fetchUserById($uid) {
    // 检查缓存中是否存在该用户信息
    $mc = new Memcached();
    $mc->addServer("127.0.0.1", 11211);
    $key = "user_".$uid;
    $data = $mc->get($key);
    if (!$data) {
        // 如果缓存中不存在该用户信息，则从数据库中查询
        $pdo = new PDO("mysql:host=127.0.0.1;dbname=mydb","root","");
        $stmt = $pdo->prepare("SELECT * FROM users WHERE id=:id");
        $stmt->bindParam(":id", $uid);
        $stmt->execute();
        $data = $stmt->fetch(PDO::FETCH_ASSOC);
        // 将查询结果缓存到Memcached中
        $mc->set($key, $data, 3600);
    }
    return $data;
}

In the above code, we use the user ID as the key name of the Memcached cache, and if the key name exists in the cache, the cached data is returned directly. Otherwise, we will query the data from the database and store the query results in Memcached so that the next query can be read from the cache.

Follow-up Thoughts

In actual applications, Memcached also has many other uses, such as page caching, session data caching, etc. Using Memcached can greatly improve the speed and performance of web applications, but at the same time, more issues need to be considered, such as cache updates, cache invalidation, cache penetration, etc. Therefore, when using Memcached for distributed caching, we need to consider its implementation process and application scenarios to improve its efficiency.

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