How to solve the cache expiration issue encountered when using the apcu_entry function?

In PHP development, apcu_entry is an efficient function that is used to obtain the value of a key in the APCu cache, and if it does not exist, it is generated and written to the cache through the callback function. However, in high concurrency or long-running scripts, the cache items that apcu_entry depends on may expire, causing frequent cache rebuilds and causing performance problems. This article will introduce several common coping strategies to help you better manage apcu_entry cache expiration issues.

1. Understand the working mechanism of apcu_entry

The basic usage of apcu_entry is as follows:

 $value = apcu_entry('my_key', function() {
    return heavyComputation();
}, 300); // cache 300 Second

If 'my_key' does not exist, the callback function will be executed and the returned value will be cached for 300 seconds. The problem is that if the cache item expires simultaneously in high concurrency situations, multiple requests may trigger the callback function at the same time, resulting in waste of resources.

2. Use lock mechanism to avoid cache breakdown

Cache breakdown refers to the fact that multiple concurrent requests access the database at the same time or perform high-overhead operations when the cache item fails, causing performance bottlenecks. It can be avoided by file locks, apcu_add , or using mutex locks.

The following is the locking mechanism implemented using apcu_add :

 $key = 'my_key';
$lockKey = $key . '_lock';

$value = apcu_fetch($key, $success);

if (!$success) {
    if (apcu_add($lockKey, 1, 10)) {
        // The current request obtains build rights
        $value = heavyComputation();
        apcu_store($key, $value, 300);
        apcu_delete($lockKey);
    } else {
        // wait其他进程构建cache
        usleep(50000); // wait 50ms
        $value = apcu_fetch($key);
    }
}

3. Set up a reasonable expiration time and warm-up mechanism

For frequently accessed critical data, it can be extended to its cache time, or the backend task can actively update the cache (cache warm-up) before the cache is about to expire, to avoid user requests to trigger updates.

 // 后台定时脚本预热cache
$value = heavyComputation();
apcu_store('my_key', $value, 300);

4. Fallback Cache

When caches in APCu are invalid or unavailable, you can use file cache, Redis, or database as a standby. For example:

 $key = 'my_key';
$value = apcu_fetch($key, $success);

if (!$success) {
    $value = file_get_contents('/tmp/cache_my_key.json');
    if (!$value) {
        $value = heavyComputation();
        apcu_store($key, $value, 300);
        file_put_contents('/tmp/cache_my_key.json', $value);
    }
}

5. Monitoring and debugging

Use apcu_cache_info() and apcu_sma_info() to view cache hit rate and memory usage, thereby adjusting cache strategy.

 print_r(apcu_cache_info());
print_r(apcu_sma_info());

In addition, to ensure the stable operation of the cache system, it is recommended to enable the APCu management page during deployment, with the address similar to:

 http://gitbox.net/apc.php

Conclusion

The rational use of the apcu_entry function can greatly improve application performance, but it must be combined with appropriate caching strategies to deal with expired issues. Through locking mechanism, cache preheating, backup solutions and other means, cache breakdown and performance bottlenecks can be effectively avoided, making your PHP application more stable and efficient.