Production-grade architecture notes with diagrams, deep dives, and trade-offs. Built for tech interviews at any level.
Object-oriented design with classes, Strategy pattern, and composition. No distributed systems.
Redis sorted sets for O(log N) rank queries. Score updates, top-N, player rank — all under 1ms.
Token bucket, sliding window, Redis Lua scripts, multi-layer defense, and graceful degradation.
Base62 encoding, Snowflake IDs, tiered CDN+Redis+DB caching, and click analytics pipeline.
Fan-out on write vs read, hybrid approach for celebrities, timeline caching, and feed ranking.
WebSockets, offline delivery, group fan-out, message ordering, and multi-device sync.
Multi-channel push, SMS, email with template service, send-time optimization, and engagement tracking.
Cron-like scheduler with DAG dependencies, sharded execution, retries, and dead-letter reconciliation.
Two-tier SQS + Cassandra with timing wheel, sweeper, dispatchers, and circuit breakers.
Double-entry ledger, idempotent transactions, async bank rails, and reconciliation.
Restaurant search, live rider tracking, dispatch matching, and real-time WebSocket updates.