{"id":2376,"date":"2026-11-03T05:00:00","date_gmt":"2026-11-03T05:00:00","guid":{"rendered":"https:\/\/www.woodcentral.com\/-\/peter\/?p=2376"},"modified":"2026-11-03T05:09:34","modified_gmt":"2026-11-03T05:09:34","slug":"using-apcu","status":"publish","type":"post","link":"https:\/\/www.woodcentral.com\/-\/peter\/using-apcu\/","title":{"rendered":"Using APCu"},"content":{"rendered":"\n

APCu is different from OPcache. While OPcache works automatically, APCu requires you to explicitly put data into the cache and retrieve it from your PHP application.<\/p>\n\n\n\n

Think of it as a small, very fast, shared-memory key-value store for PHP.<\/p>\n\n\n\n

You can use it to avoid repeatedly performing operations such as database queries, reading JSON files, generating navigation menus, or calculating frequently requested values.<\/p>\n\n\n\n

1. Basic APCu operations<\/h2>\n\n\n\n

APCu has a relatively simple API.<\/p>\n\n\n\n

Store a value:<\/p>\n\n\n\n

apcu_store('site_title', 'WoodCentral', 3600);<\/code><\/pre>\n\n\n\n
The third argument is the expiration time in seconds. Here, the value expires after one hour.<\/p>\n\n\n\n
Retrieve a value:<\/p>\n\n\n\n
$title = apcu_fetch('site_title');<\/code><\/pre>\n\n\n\n
Check whether a value exists:<\/p>\n\n\n\n
if (apcu_exists('site_title')) {\n    echo 'Cache entry exists';\n}<\/code><\/pre>\n\n\n\n
Delete a value:<\/p>\n\n\n\n
apcu_delete('site_title');<\/code><\/pre>\n\n\n\n
Clear the entire cache:<\/p>\n\n\n\n
apcu_clear_cache();<\/code><\/pre>\n\n\n\n
Be careful with apcu_clear_cache()<\/code>: it clears the user cache for the applicable APCu environment, not just one application entry.<\/p>\n\n\n\n
2. A practical example: caching a JSON file<\/h2>\n\n\n\n
Suppose your website reads a JSON file containing navigation links or other frequently accessed information.<\/p>\n\n\n\n
Without APCu:<\/p>\n\n\n\n
$data = json_decode(\n    file_get_contents(__DIR__ . '\/DATA\/links.json'),\n    true\n);<\/code><\/pre>\n\n\n\n
Every request reads and decodes the file.<\/p>\n\n\n\n
With APCu:<\/p>\n\n\n\n
<?php\n\n$file = __DIR__ . '\/DATA\/links.json';\n$key  = 'woodcentral_links';\n\n$data = apcu_fetch($key, $success);\n\nif (!$success) {\n    $json = file_get_contents($file);\n    $data = json_decode($json, true);\n\n    if (is_array($data)) {\n        apcu_store($key, $data, 3600);\n    }\n}<\/code><\/pre>\n\n\n\n
Now the JSON file is read and decoded only when the cache entry is missing or expires.<\/p>\n\n\n\n
Subsequent requests retrieve the already-decoded PHP array from shared memory.<\/p>\n\n\n\n
3. A reusable caching function<\/h2>\n\n\n\n
Rather than repeating the same logic throughout your application, you could create a small helper function.<\/p>\n\n\n\n
function wc_cache(string $key, callable $callback, int $ttl = 3600): mixed\n{\n    if (!function_exists('apcu_fetch')) {\n        return $callback();\n    }\n\n    $value = apcu_fetch($key, $success);\n\n    if ($success) {\n        return $value;\n    }\n\n    $value = $callback();\n\n    apcu_store($key, $value, $ttl);\n\n    return $value;\n}<\/code><\/pre>\n\n\n\n
Usage:<\/p>\n\n\n\n
$links = wc_cache('links', function () {\n    return json_decode(\n        file_get_contents(__DIR__ . '\/DATA\/links.json'),\n        true\n    );\n});<\/code><\/pre>\n\n\n\n
Or for a database query:<\/p>\n\n\n\n
$categories = wc_cache('categories', function () use ($pdo) {\n    return $pdo->query(\n        'SELECT * FROM categories ORDER BY name'\n    )->fetchAll(PDO::FETCH_ASSOC);\n}, 1800);<\/code><\/pre>\n\n\n\n
This is sometimes called a cache-aside pattern: the application checks the cache first and retrieves the original data only when necessary.<\/p>\n\n\n\n
4. Cache invalidation<\/h2>\n\n\n\n
One important consideration is what happens when the underlying data changes.<\/p>\n\n\n\n
For example, if you update links.json<\/code>, the cached version won’t automatically know about the change.<\/p>\n\n\n\n
You have several options:<\/p>\n\n\n\n
Expiration: Let the cache entry expire naturally.<\/p>\n\n\n\n
apcu_store('links', $data, 300);<\/code><\/pre>\n\n\n\n
Explicit invalidation: Delete the cache entry when the underlying data changes.<\/p>\n\n\n\n
apcu_delete('links');<\/code><\/pre>\n\n\n\n
File modification time: Automatically invalidate when a file changes.<\/p>\n\n\n\n
$file = __DIR__ . '\/DATA\/links.json';\n\n$key = 'links_' . filemtime($file);\n\n$links = wc_cache($key, function () use ($file) {\n    return json_decode(file_get_contents($file), true);\n});<\/code><\/pre>\n\n\n\n
The last approach is particularly useful for file-based applications.<\/p>\n\n\n\n
5. APCu versus OPcache<\/h2>\n\n\n\n
Feature<\/th>APCu<\/th>OPcache<\/th><\/tr>
Stores PHP application data<\/td>Yes<\/td>No<\/td><\/tr>
Stores compiled PHP scripts<\/td>No<\/td>Yes<\/td><\/tr>
Requires application code<\/td>Yes<\/td>No<\/td><\/tr>
Uses shared memory<\/td>Yes<\/td>Yes<\/td><\/tr>
Survives PHP\/server restart<\/td>No<\/td>No<\/td><\/tr>
Useful for JSON caching<\/td>Yes<\/td>No<\/td><\/tr>
Useful for database results<\/td>Yes<\/td>No<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
They complement one another rather than compete.<\/p>\n\n\n\n
6. A few things to understand<\/h2>\n\n\n\n
There are some practical limitations:<\/p>\n\n\n\n