System Design · Pinterest · Hard
Every ad-supported platform must answer the same fundamental question: which ad should we show in this slot, to this user, at this moment? The answer must weigh what an advertiser is willing to pay against how likely the user is to engage, and it must do so billions of times per day in under 50 milliseconds. Get it right and you have a revenue engine that funds the entire product. Get it wrong and advertisers overpay, users see irrelevant ads, and the marketplace loses trust…
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