Google Search: Crawling, Indexing, & The PageRank Algorithm
Search the entire web: Googlebot distributed crawler, Inverted Index shard distribution, PageRank link graph scoring, and sub-50ms query serving.
01.The Scale of Web Search & Distributed Web Crawling
Google Search indexes hundreds of billions of web pages (exabytes of text and metadata) and processes over 8.5 billion searches per day while returning highly relevant results in < 50 milliseconds.
The foundational lifecycle of search begins with Distributed Web Crawling (Googlebot):
- The Crawl Frontier: A distributed priority queue holding trillions of discovered URLs. The frontier prioritizes URLs based on expected page refresh frequency, domain importance, and historical PageRank.
- Host Politeness & Rate Limiting: Crawlers must avoid overwhelming web servers (which would constitute a denial-of-service attack). Googlebot enforces strict per-host rate limits, checks
robots.txtrules, and caches DNS lookups. - SimHash / MinHash Content Deduplication: The web is filled with identical syndicated articles and mirrored content. Googlebot calculates 64-bit SimHash locality-sensitive fingerprints of page text, identifying near-duplicate documents without storing redundant index entries.
- JavaScript Rendering (Headless Chrome): Because modern websites rely heavily on client-side rendering (React, Angular), Googlebot executes JavaScript in a massive distributed headless browser fleet before extracting text and links.
Google Search: End-to-End Crawling, Indexing, & Sub-50ms Query Pipeline 🔍
Google Search: End-to-End Crawling, Indexing, & Sub-50ms Query Pipeline 🔍
Parallel fan-out execution across thousands of in-memory inverted index shards with PageRank and BERT semantic ranking.
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