How to implement cache dependency management through apcu_entry and custom tags

In cache management, especially when multiple cache items depend on each other, we usually need a way to track these dependencies. When a cache item changes, we want to be able to automatically update the cache associated with it. At this point, custom tags provide an elegant solution.

1. Use tags to manage cache updates

By introducing custom tags, we can specify a dependency tag for each cache item. These tags are used to indicate the dependency between cache items and other cached data. Suppose we have a set of cached data items that depend on the state of an external resource (for example, the content of a database table changes).

First, we can create a function to store cached data and introduce dependency tags in it:

 function storeWithDependencies($key, $data, $dependencyKey) {
    // Save data into cache
    apcu_store($key, $data);
    
    // Update dependency markers for cache items
    apcu_store($dependencyKey, time());  // Use timestamps as markers
}

In this example, the storeWithDependencies() function updates a dependency tag in addition to storing data. By using timestamps as dependency markers, it is possible to ensure that when the mark changes, the relevant cache items will also be updated.

2. Determine whether the cache needs to be updated

When getting cached data, we need to check if there is any change in the dependency marker. If the tag changes, we can regenerate the cached data.

 function fetchWithDependencies($key, $dependencyKey) {
    // Get the current dependency marker
    $lastDependencyUpdate = apcu_fetch($dependencyKey);
    
    // Get cached data
    $cachedData = apcu_fetch($key);
    
    // If the cached data does not exist or the dependency marker has been updated，Recalculate and store the cache
    if ($cachedData === false || $lastDependencyUpdate < getLastDataUpdateTime()) {
        $cachedData = getSomeDataFromDb();
        apcu_store($key, $cachedData);
        apcu_store($dependencyKey, time());
    }
    
    return $cachedData;
}

In this code, the fetchWithDependencies() function checks whether the cached data exists and compares whether the dependency marks have changed. If the dependency tag changes (such as the database table is updated), the cache data is recalculated and the cache and tags are updated.

Cache management policy combining apcu_entry and custom tags

By combining the apcu_entry() function and custom tags, we can achieve more efficient and flexible cache dependency management. When cache dependencies change, the new cache will be automatically updated, avoiding expired or invalid data affecting application performance.

For example, we can use the following strategy in a cache system with complex dependencies:

 function fetchWithComplexDependencies($key, $dependencyKey) {
    // use apcu_entry to obtain or calculate cached data
    return apcu_entry($key, function() use ($dependencyKey) {
        // Check if dependency markers have changed
        if (apcu_exists($dependencyKey)) {
            $lastUpdate = apcu_fetch($dependencyKey);
            if ($lastUpdate < getLastDataUpdateTime()) {
                // Data has been updated，Need to be reacquisitioned
                return getSomeDataFromDb();
            }
        }
        
        // The cached data has not changed，Return to existing cache
        return apcu_fetch($key);
    });
}

In this example, apcu_entry() is used to handle access to cached data, while dependency tags control when the cache is recalculated. In this way, when an external dependency changes, the cache system can be updated in time to ensure that the latest data is obtained.