Two Hard Things: caching bugs

There are only two hard things in computer science, and cache invalidation is the one that pages you at 3 AM. This series takes the bugs I have actually watched take production down, one per minute: the write that races the cache, the delete that is not enough, the hot key whose expiry stampedes the database, the TTLs that all expire on the same schedule, and the “not found” nobody thought to cache.

Each part names the failure, shows why it happens, and ends on the boring fix that works. Watch them in order: every part assumes the cache from the one before.