Candidate generation
What COULD show? Posts from follows + suggested + reels + explore. Hundreds of candidates per user per request.
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Candidate generation
What COULD show? Posts from follows + suggested + reels + explore. Hundreds of candidates per user per request.
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ML ranking
Predict engagement (like/comment/save/dwell time) per candidate per user. Top scores make the feed.
Diversification
Prevent 5 in-a-row from same person. Mix photos + reels + stories. Keeps feed interesting.
TAO for graph
Social graph service (Facebook infra). Millions of QPS. Cached aggressively. Powers follows + likes reads.
Media serves from CDN
Photos/videos never come from feed service. Feed returns URLs; client fetches from edge cache. Massive bandwidth saved.