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As web-scale indexing and scraping become more resource-constrained and privacy-conscious, simple heuristics for link selection remain valuable. nthlink is a pragmatic approach: instead of following every hyperlink on a page, a crawler follows every nth link (or a variant such as “every nth unique domain link”), reducing bandwidth, storage, and processing costs while still discovering a representative set of pages. What nthlink means At its core, nthlink is the rule “follow the k-th, 2k-th, 3k-th, … link,” where k is a configurable integer. On a page with many links, this immediately throttles propagation. Variations include: - Offset nthlink: start at an offset m and follow links m, m+k, m+2k (useful to distribute load across runs). - Weighted nthlink: apply nth selection only to lower-priority link regions (e.g., footer or sidebar). - Domain-aware nthlink: count links per domain and follow every nth link within each domain to ensure domain diversity. - Randomized nthlink: add a small random jitter to k or m to reduce systematic bias. Why use nthlink - Cost control: Reduces number of requests and storage requirements linearly with k. - Diversity: By sampling instead of exhaustively crawling, you can prioritize broader coverage over depth in early discovery phases. - Simplicity: Easy to implement and reason about, making it attractive for prototypes and constrained environments. - Politeness: Fewer requests per site can be friendlier to target servers and easier to schedule. When it falls short nthlink is a heuristic and can miss important or narrowly linked content if important links aren’t evenly distributed. It introduces bias toward link ordering (which might reflect layout or editorial priorities). It’s not a substitute for targeted crawling when coverage completeness is required. Implementation tips - Respect robots.txt and rate limits; nthlink is an orthogonal optimization, not a permission. - Combine nthlink with link scoring (anchor text, URL patterns, prior knowledge) so high-value links override sampling. - Use offsets or randomization when crawling the same domain repeatedly to avoid systematic omissions. - Monitor discovery metrics (new pages per crawl, domain coverage) and adjust k adaptively. - Consider hybrid approaches: use nthlink for breadth-first discovery, then focused crawls for deep coverage of high-value targets. Example (conceptual) For k = 3, offset m = 2: follow links at indexes 2, 5, 8, 11… Adaptive tuning can lower k for under-explored domains and raise k for heavily sampled ones. Conclusion nthlink is a low-complexity, high-impact tool in the crawler designer’s toolbox. Used judiciously and combined with heuristics or learning-based ranking, it delivers efficient, polite, and broad discovery suitable for many large-scale scraping and indexing problems.