System design interview question
"Design real-time fraud detection for a payments platform. Every transaction must be scored and approved or declined within about 100 milliseconds, using signals about the card, the device, the merchant, and the user's history. Fraudsters adapt within days."
low-latency feature computation on streaming data, plus the adversarial dynamics that distinguish fraud from ordinary ML systems. The distinguishing content is: a hard latency budget that rules out expensive lookups, the combination of rules and models, feedback labels that arrive weeks late, and the fact that your adversary responds to your defences.
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