News Feed / Timeline

Reads happen ~20× more often than writes. If you query every followee's posts on every feed load, you pay O(N) DB queries per read. Fan-out on write flips this: push each new post_id into every follower's Redis list at write time so reads are a single O(1) cache lookup. Celebrities get a hybrid pull model to avoid writing to 300M lists on a single post.

← Tap the heart button to begin