[00:01] Taylor Swift to post to her 300 million followers? One solution is to keep a cache for each user. The post gets pushed into each follower's cache immediately. Then we can read from that cache almost instantly when they load
[00:14] the app. Great. Or until you have 300 million followers. A single post triggers 300 million cache writes at once. That write storm takes minutes to propagate and can spike server load to catastrophic levels. So,
[00:29] let's use a hybrid approach. Regular users still get fan out on write. Their posts are precomputed into their followers feed caches. For celebrities, we can special case them in our system. When users load their feeds, they'll
[00:42] celebrities they're following. This makes the right load stay flat no matter what Taylor does. The tradeoff is slightly more complex read logic, but feed latency stays under 500 milliseconds because the celebrity merge
[00:57] is a small operation on top of an already cached feed. There's no universally correct fan out strategy. The right answer depends on the data your system is handling. That's the kind of nuance that separates a good system
[01:10] design from a great. Like and follow us for more system design tips.