Senior interview questionAsked at Pinterest · interview write-up
Design a real-time home feed ranker that blends long-term personalization with streaming engagement signals, at low latency.
Model answer
A funnel with a latency budget per stage. Retrieval pulls a few thousand candidates from several sources: ANN over item embeddings using a daily long-term user embedding, plus candidates seeded by the user's last few actions. A light pre-ranker trims them; a multi-task ranker predicts save, click and hide, combined into one score; a blender enforces diversity and freshness.
Streaming events update a recent-action sequence in the online feature store within seconds; the ranker reads it alongside long-term features. Log features as served, so training matches serving. Judge by A/B tests.
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