System design interview question
"Design a web crawler. It discovers URLs, fetches pages, extracts links, and keeps going. It should crawl billions of pages, stay fresh, and — importantly — not get you blocked or sued. Design it."
politeness and scheduling under adversarial and legal constraints, not raw throughput. Fetching pages fast is easy; the hard parts are per-domain rate limiting, URL deduplication at billion scale, crawl-frequency prioritization, and traps. A candidate who designs a fast fetcher and ignores politeness has designed something that gets blocked in an hour.
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