System design interview question
"Design a price tracking service. Users pick products on retail sites and get alerted when the price drops below a threshold. You show price history charts going back years. You do not have an API — you read prices from public web pages, and the retailers would rather you did not."
scheduling scarce, unreliable work against an adversarial source. You cannot check every product often; you are blocked if you try; and the data you get is untrustworthy. The discriminating insight is that crawl budget must be allocated by expected value, not uniformly.
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