CodeIgniter 4 cache invalidation limits without tagging support

Implementing Bulk Invalidation Without Tags

CodeIgniter 4 does not provide a native mechanism for bulk invalidation or wildcard clearing for drivers that do not implement the TaggableInterface (such as the File driver). To achieve group invalidation without manually tracking every key, the most effective documented pattern is Key Versioning.

The Key Versioning Pattern

Instead of attempting to delete multiple keys, you introduce a version identifier into the cache key itself. When the underlying data changes, you increment the version number, effectively rendering all previous cache entries for that group obsolete.

1. Store a version key: Save a simple integer or timestamp in the cache (e.g., 'user_profile_version').
2. Generate dynamic keys: Append this version to your data keys: 'user_profile_v' . $version . '_' . $userId.
3. Invalidate the group: To "clear" all user profiles, simply increment the 'user_profile_version' value. The application will then look for keys with the new version, and the old files will naturally expire via their TTL.

File Driver Concurrency and Race Conditions

The File driver handles cache entries as individual files on disk. It is important to understand its behavior during high-concurrency write operations:

• Atomic Writes: CodeIgniter typically writes to a temporary file and then moves it to the final destination to prevent partial reads.
• Stale Reads: Because there is no distributed locking mechanism in the File driver, a "race to write" can occur. If two processes update the same key simultaneously, the last one to complete the move operation wins.
• Consistency: There is no guarantee of immediate consistency across multiple requests during a write. A process may read a stale file milliseconds before it is overwritten by another process.

Verification Steps

To verify if your current configuration supports tagging, check app/Config/Cache.php. If the $handler is set to 'file', any attempt to use tagging methods will fail or be ignored.

// Example of Key Versioning implementation
$version = cache()->get('blog_version') ?? 1;
$cacheKey = "blog_posts_v{$version}";
$data = cache()->get($cacheKey);

// To invalidate all blog posts:
cache()->inc('blog_version');

Diagnostic Detail Required: Are you utilizing a shared filesystem (like NFS) for your File driver across multiple web servers? This significantly changes the risk profile for race conditions and file locking.