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System Design for Python Juniors
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Module 6 · Real-World System Design Cases
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Design Spotify recommendations
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📝 **Question:** Why mix offline and online recommendation steps? 📋 Pick the right answer. 💡 **Hint:** Re-read the theory above if unsure.
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Question
📝 **Question:** Why mix offline and online recommendation steps? 📋 Pick the right answer. 💡 **Hint:** Re-read the theory above if unsure.
A
Online inference is too slow for 600M users — batch computes the full ranked playlist nightly so the app just reads a static list at session start.
B
Offline computes heavy candidate generation in batch; online re-ranks the top 200 with fresh per-user signals (mood, time of day, recent skips).
C
Offline trains the model; online serves the exact same scores without re-ranking — splitting just isolates training infra from serving infra for ops reasons.
D
Online handles cold-start users while offline handles power users — each pipeline owns one population and they never overlap during a session.
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