Facebook News Feed — Notes

Functional

• Aggregate posts from friends, pages, groups, recommendations.
• Rank by relevance (Meaningful Social Interactions).
• Inject ads at known positions.
• React, comment, share, save, hide.

Non-functional

• 3B+ MAU. Feed open p99 < 300 ms.
• Multi-region active-active for reads.

Capacity

• Posts/day: ~5B (incl. comments, reacts).
• Reads/day: 100B+.
• Feed compute: thousands of features × millions of candidates evaluated per session.

Schema (conceptual)

• TAO objects: user, post, page, group, photo.
• TAO assocs: friends, likes, follows, posted.
• Posts in sharded SQL by owner_id.
• Aggregations precomputed and cached.

Trade-offs

• Pull-aggregator is more expensive per read but doesn't suffer the celeb fan-out problem.
• TAO sacrifices some consistency for cross-region read latency.
• Heavy ML demands GPU/TPU; staged ranking (cheap candidate gen → expensive scorer).
• Privacy & integrity complexity dwarfs the ranking complexity.

Refs

• Facebook TAO paper (USENIX ATC '13).
• Haystack (small photo storage) paper.
• "How News Feed Works" engineering posts.
• ByteByteGo & Alex Xu Vol 2.