How PhpFastCache solves cache avalanche problem

How PhpFastCache solves the cache avalanche problem

Introduction:
Caching is a technology we commonly use to improve system performance. When the number of concurrent accesses increases and the cache is frequently penetrated or expired, a large number of requests will directly access the data source, resulting in excessive database load, which may eventually lead to a system crash. This phenomenon is called the Cache Avalanche problem. PhpFastCache is a PHP caching library that provides a solution to the cache avalanche problem.

Cause of cache avalanche problem:
When the cache server goes down or is restarted, the cache server may fail at the same time, causing a large number of new requests to directly access the data source. These requests will access the database at the same time. Due to the surge in concurrency, the database cannot withstand the pressure, causing the system to crash. In addition, when the cache expiration time is the same, the data will also be invalidated at the same time, causing a cache avalanche problem.

PhpFastCache's method of solving the cache avalanche problem:
PhpFastCache solves the cache avalanche problem by using random expiration time and mutex locks.

Sample code:

use PhpFastCacheCorePoolExtendedCacheItemPoolInterface;
use PhpFastCacheCacheManager as CacheManager;

// 配置缓存驱动
CacheManager::getDefaultInstance()->setDriver('files');

// 获取缓存对象
$cache = CacheManager::getInstance();

// 设置缓存
$cache->setExtendedCacheItem('my_cache_key', 'my_cache_value', 60);

// 获取缓存
$value = $cache->get('my_cache_key');
if ($value == null) {
    // 缓存失效，从数据源获取数据
    $value = getDataFromDataSource();
    // 设置缓存并设置随机的过期时间
    $cache->set('my_cache_key', $value, rand(60, 120));
}

//从数据源获取数据的方法
function getDataFromDataSource(){
   //获取数据源的数据
}

In the above code example, we use the cache manager of PhpFastCache to read and write the cache. When setting up the cache, we set a random expiration time to avoid cache invalidation at the same time. When the cache expires, we fetch the data from the data source and set a random expiration time, which can spread out the data update requests.

In addition to setting a random expiration time, PhpFastCache also provides a mutex lock function to solve the cache avalanche problem. In a multi-threaded environment, locking can ensure that only one thread can query the database, and other threads will wait for the lock to be released before querying.

Sample code:

// 获取缓存
$value = $cache->get('my_cache_key');
if ($value == null) {
    // 上锁
    $cache->lock('my_cache_key');
    // 再次判断缓存是否为空
    $value = $cache->get('my_cache_key');
    if ($value == null) {
        // 缓存失效，从数据源获取数据
        $value = getDataFromDataSource();
        // 设置缓存并设置随机的过期时间
        $cache->set('my_cache_key', $value, rand(60, 120));
    }
    // 解锁
    $cache->unlock('my_cache_key');
}

In the above example code, we first try to get the cache. If the cache is empty, we will lock it first, and then judge again whether the cache is empty. During the locking period, other threads will wait for the lock to be released. If the cache is still empty, we get the data from the data source and set the cache, and finally unlock it. This ensures that only the first thread to obtain the lock can query the database, while other threads will wait for the cache to be updated before querying.

Summary:
By using the random expiration time and mutex lock methods provided by PhpFastCache, we can effectively solve the cache avalanche problem. In practical applications, we can choose appropriate methods according to specific scenarios to solve the cache avalanche problem and improve system stability and performance.

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