How to Install and Use PHP APCu for High‑Performance Caching

Overview

PHP APCu (Advanced and Performance Caching User Cache) is a shared‑memory cache for PHP 5.5+ that provides a user‑level caching mechanism. It is a branch of APC without OPcache.

Features

Shared‑memory cache : multiple PHP processes can access the same cached data, improving performance.

User cache : stores session data and application‑level caches, not compiled PHP code.

Simple API : functions such as apcu_store(), apcu_fetch(), apcu_add(), and apcu_delete() handle cache operations.

Performance boost : reduces database queries and file I/O by caching frequently accessed data.

Memory management : automatically evicts old entries when memory is low.

Process isolation : cache data is isolated per PHP process, enhancing security.

Configuration : parameters like cache size and cleanup policy are set in php.ini.

Installation

Download and extract the source package:

wget https://pecl.php.net/get/apcu-5.1.23.tgz
 tar -zxvf apcu-5.1.23.tgz

Prepare the build environment:

cd apcu-5.1.23
 /usr/local/php-7.4/bin/phpize

Configure the extension (use sudo if permission errors occur):

./configure --with-php-config=/usr/local/php-7.4/bin/php-config

Compile and install:

sudo make -j4
 sudo make install

Verify that apcu.so appears in the PHP extensions directory, then enable it in php.ini:

[apcu]
 extension=apcu.so
 apc.shm_size=1024M

Check the installation:

php -i | grep apcu

Simple Usage

Example script that writes and reads 10,000 keys:

<?php
$start = microtime(true);
for ($i = 0; $i < 10000; $i++) {
    $key = 'apcu' . $i;
    apcu_add($key, $i); // fails if key exists, similar to Redis SETNX
    apcu_fetch($key);   // returns false if not found
}
echo microtime(true) - $start . PHP_EOL;

Typical runtime on a test machine is around 0.001 seconds.

Performance Comparison with Redis

Read‑only (10 k ops): APCu 0.011 s vs Redis 1.162 s

Write‑only (10 k ops): APCu 0.012 s vs Redis 1.062 s

Read/Write with a single Redis connection: APCu 0.011 s vs Redis 2.117 s

Read/Write with multiple Redis connections: APCu 0.011 s vs Redis 3.646 s

The benchmark shows that APCu provides dramatically lower latency for in‑process caching compared with Redis, making it suitable for fast local data storage in PHP applications.