Memcached caching technology supports high availability of PHP applications

Memcached caching technology supports high availability of PHP applications

With the rapid development of the Internet, the requirements for Web applications are becoming higher and higher. Among them, high availability is one of the issues that users are most concerned about. In high-traffic application scenarios, traditional database read and write operations can no longer meet the requirements for high concurrency and high performance. The application of caching technology has long become one of the necessary components in web applications. Memcached is a widely used open source caching software that can significantly improve the performance of web applications. This article will focus on the application of Memcached caching technology in high availability of PHP applications.

1. Overview of Memcached

Memcached is a high-performance, distributed memory object caching system that can be used to reduce the load on data storage backends such as databases. Its official definition is as follows:

"Memcached is a high-performance distributed memory object caching system, often used to accelerate dynamic web applications, such as PHP, etc. It stores data in memory to Provides fast storage and retrieval, as well as reducing the load on data storage backends (such as databases)."

Memcached can store data completely in memory. Compared with data storage backends such as databases, its operation speed is Much faster. At the same time, due to its distributed characteristics, multiple Memcached nodes can form a cluster, and can form data replication, load balancing and other mechanisms between each other, which can better ensure the availability and performance of the system. The architecture diagram of Memcached is as follows:

2. Application of Memcached in PHP

Applying Memcached caching technology in PHP can cache MySQL, Redis, MongoDB and other database operations, or Directly cache the page output content and other operations. By using Memcached, the performance of your application can be significantly improved. Two specific application scenarios are introduced below.

1. Database cache

In applications, there are often SQL operations such as SELECT, UPDATE, INSERT, and DELETE. At this time, you can use Memcached to cache query results and reduce the need for database operations. number of visits. This can not only improve performance, but also avoid database crashes or other abnormal situations that prevent the application from providing normal services. The specific implementation is as follows:

<?php

$mem = new Memcache();
$mem->connect("localhost", 11211);

$key = md5("SELECT * FROM user WHERE id=1");

$result = $mem->get($key);

if (!$result) {
    $mysqli = new mysqli("localhost", "user", "password", "database");
    $query = "SELECT * FROM user WHERE id=1";
    $result = $mysqli->query($query)->fetch_assoc();

    $mem->set($key, $result, 0, 3600);
}

print_r($result);

?>

This code first uses Memcached to obtain cached data. If the cache does not exist, it obtains the data from the database and stores the result in Memcached. Among them, the third parameter is the expiration time. If it is 0, it means that the data will never expire. The fourth parameter is the storage time, that is, the cache time, in seconds.

2. Page output cache

In the page output of the application, there are some contents that do not need to be regenerated every time, such as home page, category page, etc. At this time, the content of these pages can be cached through Memcached to reduce the pressure on the front-end web server and back-end application server, and also improve the response speed of user access. The specific implementation is as follows:

<?php

$mem = new Memcache();
$mem->connect("localhost", 11211);

$key = md5("index");

$result = $mem->get($key);

if (!$result) {
    ob_start();

    // 生成首页内容
    include("index.php");

    $result = ob_get_contents();

    ob_end_flush();

    $mem->set($key, $result, 0, 3600);
}

echo $result;

?>

Before generating the homepage content, this code first uses the ob_start() function to enable caching. After generating the page content, it uses the ob_get_contents() function to obtain the cached results, and uses the ob_end_flush() function to output HTML. content. If the cache does not exist, the page content is generated and the results are stored in Memcached.

3. Summary

Memcached is a high-performance, distributed memory object caching system that can significantly improve the performance of web applications and is also very important for high-availability support for PHP applications. . When using Memcached, you need to pay attention to the following points:

1. Data consistency issues. Since Memcached is distributed, data synchronization between multiple nodes takes time, so when storing and retrieving data, a certain mechanism needs to be used to ensure data consistency.
2. Memory consumption problem. Since Memcached is completely based on memory, you must pay attention to controlling the use of memory to avoid system paralysis caused by excessive memory usage.
3. Caching strategy issue. Caching strategies such as cache time and cache key values ​​need to be reasonably set based on actual business scenarios and characteristics.

This article starts from the concept and characteristics of Memcached, and introduces the application scenarios and implementation methods of Memcached in high availability of PHP applications. In practical applications, Memcached can not only improve the performance and availability of web applications, but also help users better maintain web applications.

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