How to avoid cache avalanche problem in PHP?

How to avoid cache avalanche problem in PHP?

In web applications, caching is often used to improve performance and reduce server load. When multiple requests request a cache key at the same time, and the cache key has the same expiration time, a cache avalanche problem may occur. The cache avalanche problem means that all requests for this cache key at the same time will fall on the database. Due to the excessive request load, the server will crash or fail.

Let’s talk about how to avoid the cache avalanche problem in PHP:

1. Set the cache expiration time to be random

We can set the expiration time of each cache key to be random Different, avoid all cache keys from being invalidated at the same time. PHP's random_int() can generate random numbers. Setting the expiration time based on this random number can effectively avoid cache avalanche problems.

// 生成随机数作为缓存时间，并设置缓存
$ttl = random_int(60, 600);
Cache::set($key, $value, $ttl);

2. Monitor the status of cache keys

We can use a monitor command similar to that provided by Redis to record all commands and response information communicating with the Redis server, and then capture cache key expiration in the monitoring data moment, thereby refreshing the cache key in a timely manner. This approach can greatly reduce performance issues caused by cache invalidations.

3. Automatic cache preheating

Preheating the cache can ensure that before the cache expiration time arrives, we can query the database in advance and obtain the latest data, and then set the data into the cache. This is to avoid all requests flooding into the database when the cache fails, causing slow server response.

// 将数据添加到缓存中
Cache::set($key, $value, $ttl);

// 预热缓存
$preheatTTL = 3600;
Cache::set($key, $value, $preheatTTL);

4. Add cache mutex

When multiple requests obtain a cache key at the same time and the cache key has expired, one of the requests should be sent to query the database and obtain the latest data. , and set it to the cache, and other requests will obtain data from the cache to reduce database requests. At this time, a cache mutex needs to be added to prevent multiple requests from querying the database at the same time, causing excessive load.

// 添加缓存互斥锁
$lock_key = $key . ':lock';
if(!Cache::add($lock_key, 1, 1)){
    // 缓存正在被刷新
    return;
}

// 查询数据库并获取最新数据
$value = db_query();

// 将数据设置到缓存中，并释放缓存互斥锁
Cache::set($key, $value, $ttl);
Cache::delete($lock_key);

Summary

The cache avalanche problem is a problem often encountered in cache use. It is usually used to set random expiration time, monitor cache key status, automatically warm up the cache, add cache mutex locks, etc. way to solve it. In actual use, a combination of these methods can effectively avoid cache avalanche problems based on specific circumstances.

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