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CRDT: Conflict-Free Replicated Data Types CRDTs are data structures that guarantee strong eventual consistency: any two replicas that have received […]

URL Frontier Priority queue of URLs to crawl, prioritized by PageRank estimate + freshness. CrawlJob Table CrawlJob ( id, url,

Sitemap XML Format urlset with url entries: loc, lastmod, changefreq, priority. Sitemap Index For sites with >50K URLs, generate multiple

Data Model CheckJob Table CheckJob ( id, target_domain, status: queued/running/completed, started_at, completed_at, total_links, broken_count ) LinkResult Table LinkResult ( id,

Query Syntax A full-featured query parser supports: AND/OR/NOT boolean operators, phrase queries (exact ordered match), field-specific search (title:python), wildcards (*

Invoice Service: Overview An invoice service manages the full lifecycle of invoices: creation, line items, tax, PDF generation, payment collection,

Double-Entry Accounting Primer Every financial event produces at least two journal lines: one debit and one credit. The sum of

Overview A payout service disburses funds to recipients via multiple rails: ACH (batch, 1-2 day settlement), wire (same-day, high fee),

Feature Flag Targeting Service: Low Level Design A feature flag targeting service lets teams release features safely by controlling visibility

Experimentation Platform: Low Level Design An experimentation platform enables A/B and multivariate tests with rigorous statistical guarantees. This design covers

ML Model Serving Service: Low Level Design An ML model serving service provides versioned, low-latency online inference alongside batch prediction,

OT for Text Operations are insert(pos, text) and delete(pos, len). Transformation Function transform(op1, op2) adjusts positions of concurrent ops to

Cursor State { user_id, user_name, color, position: { line, col } // for text, or { x, y } for

Overview An ML-powered content moderation service classifies user-submitted content (text, images, video) at scale, routes borderline cases to human reviewers,

Quiz Engine Data Model A quiz engine supports timed assessments, randomization, auto-grading, leaderboards, and anti-cheat mechanisms. Core Tables Quiz (id,