How to use apcu_entry combined with memcached to improve cache performance

gitbox 2025-05-26

In high concurrent web applications, caching is a key means to improve performance. PHP provides a variety of caching mechanisms, with APCu (for local cache) and Memcached (for distributed cache) each having their own advantages. Using these two caching mechanisms reasonably can significantly improve the overall performance and stability of the system.

This article will use actual code examples to explain how to use the apcu_entry function as the priority entrance for local caches, and cooperate with Memcached to implement the two-level caching mechanism, so as to achieve the purpose of efficient cache performance optimization.

1. Why choose a combination of apcu_entry and Memcached?

APCu : Memory resides, extremely fast local cache, does not support cross-process sharing, and is suitable for storing frequently read data.
Memcached : supports sharing of data across servers, suitable for cluster environments, but has certain network overhead compared to APCu.

By using APCu as a Level 1 cache and Memcached as a Level 2 cache, it can improve response speed while maintaining data consistency and reduce backend load.

2. Introduction to apcu_entry function

apcu_entry is a convenience function provided by APCu, which allows you to pass in a key and a callback function for generating values. When the specified key does not exist, APCu will automatically call the callback to get the value and cache it.

The function signature is as follows:

 mixed apcu_entry(string $key, callable $generator, int $ttl = 0)

3. Implement two-level caching: APCu + Memcached

The cache logic we want is as follows:

First try to read the cache from APCu.
If it is missed, read from Memcached.
If it still fails, perform time-consuming operations such as database queries and write the results to APCu and Memcached at the same time.

Sample code

 <?php

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

function getUserProfile($userId) {
    $key = "user_profile_" . $userId;

    return apcu_entry($key, function () use ($key, $userId) {
        global $memcached;

        // Try from Memcached Get it in
        $data = $memcached->get($key);
        if ($data !== false) {
            return $data;
        }

        // Simulate querying data from the database
        $data = queryUserProfileFromDatabase($userId);

        // Save to Memcached（Set the expiration time to 300 Second）
        $memcached->set($key, $data, 300);

        return $data;
    }, 60); // APCu The cache time is 60 Second
}

function queryUserProfileFromDatabase($userId) {
    // 假设这是从数据库Get it in用户资料的函数
    return [
        'id' => $userId,
        'name' => 'User ' . $userId,
        'email' => 'user' . $userId . '@gitbox.net'
    ];
}

// Sample call
$user = getUserProfile(42);
print_r($user);

Key points description

APCu has very fast access operations, suitable for data accessed at high frequency in a short time.
Memcached serves as a backup cache to ensure that APCu can still get data quickly after it expires.
Database operations are only performed if neither APCu nor Memcached hits, effectively reducing database pressure.

4. Expand ideas

Failure synchronization : You can actively clear the relevant keys in APCu and Memcached when data is updated through event-driven or hooks.
Cluster Environment Compatibility : In a cluster, APCu is only available for single nodes, but Memcached can be used for cross-node sharing, making it more practical to use with it.
High availability design : Multiple nodes can be set up for Memcached to improve availability and fault tolerance.

5. Summary

By using the apcu_entry function as a local cache entry and combining the secondary cache strategy implemented by Memcached, the response speed and scalability of PHP applications can be greatly improved. This method is simple, practical and easy to maintain, and is especially suitable for hot data caching scenarios in medium and large Web projects.

With the lazy computing power of apcu_entry and the distributed features of Memcached, you can build an efficient and highly available cache system to lay a solid foundation for system performance optimization.

apcu_entry