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In PHP, APCu (Alternative PHP Cache User) is a widely used caching extension that significantly improves data access speed. apcu_clear_cache and apcu_fetch are two essential functions in APCu: the former clears the cache, while the latter retrieves data from the cache. This article focuses on the combined use of these two functions, emphasizing the key points to watch out for in practical development.
apcu_clear_cache() clears all cached items in the current process (typically the APCu cache shared by all user requests). This means:
Once called, all cached data is immediately wiped.
It is suitable when a complete refresh of the data structure is needed but should not be called frequently.
Key point: Frequent calls to this function cause cache to expire often, increasing pressure on databases or other backend resources and ultimately reducing performance.
apcu_fetch($key, &$success) attempts to fetch data associated with the specified key from the cache. It has a crucial parameter $success to indicate whether the data retrieval was successful.
Example:
<?php
$key = 'user_data';
$data = apcu_fetch($key, $success);
if ($success) {
// Successfully read from cache
echo "Cached data: " . json_encode($data);
} else {
// Cache miss, execute logic to retrieve fresh data
$data = getUserDataFromDB();
apcu_store($key, $data);
}
?>
Key point: Always check $success, because apcu_fetch may return false if not found, but the cached data itself could also be false. Relying solely on the return value could mistakenly interpret a cache hit as a miss.
Suppose you use apcu_clear_cache() to clear all caches and then use apcu_fetch() to retrieve data. In this case, a cache miss may occur, requiring you to fetch data again from the data source and write it back to the cache.
Example:
<?php
// Clear cache
apcu_clear_cache();
<p>// Fetch data<br>
$data = apcu_fetch('my_key', $success);<br>
if (!$success) {<br>
// Cache is empty; need to fetch from DB or other source<br>
$data = getDataFromSource();<br>
apcu_store('my_key', $data);<br>
}<br>
echo $data;<br>
?><br>
Key points:
Clearing the cache should be done cautiously and not frequently.
After clearing, rebuild necessary caches promptly to avoid cache stampede.
In multi-threaded or multi-process environments, race conditions may arise during cache rebuilding; locking or distributed lock strategies are recommended.
APCu is a shared memory cache theoretically shared by all PHP processes on the same server. However, in multi-server or multi-process setups, apcu_clear_cache() only affects the cache on the current server and cannot synchronize cache clearing across other servers.
Key points:
In distributed environments, relying solely on APCu cache clearing may lead to data inconsistency.
It is recommended to use distributed cache solutions like Redis or Memcached, or design your own cache synchronization mechanism.
When using apcu_fetch and apcu_clear_cache, good cache key naming helps avoid accidental cache clearing.
<?php
// Cache user data to avoid conflicts with other caches
$key = 'user_data_' . $userId;
$data = apcu_fetch($key, $success);
?>
Key points:
Avoid using generic cache keys that might cause unrelated data to be cleared unintentionally.
Instead of frequently clearing all caches, it’s better to use apcu_delete to delete specific keys.
apcu_clear_cache clears all caches and should be used cautiously.
When using apcu_fetch, always check the $success parameter to avoid misjudgment.
After clearing cache, rebuild caches promptly to prevent cache stampede.
APCu does not support cross-server cache synchronization in multi-server environments.
Name cache keys carefully and prefer precise deletion with apcu_delete.
Properly combining apcu_clear_cache and apcu_fetch and designing effective cache invalidation and rebuilding mechanisms are key to ensuring efficient cache usage.
<?php
// Example: Using apcu_clear_cache and apcu_fetch together
apcu_clear_cache();
<p>$key = 'gitbox.net_cache_key';<br>
$data = apcu_fetch($key, $success);</p>
<p>if (!$success) {<br>
$data = "Data reloaded from the data source";<br>
apcu_store($key, $data);<br>
}</p>
<p data-is-last-node="" data-is-only-node="">echo $data;<br>
?><br>
