Low-Level Design: Code Review Tool – Diffs, Comments, Approvals, and CI Integration (2025)
Core Entities Diff Computation Server-side diff using the Myers diff algorithm (also used by git). Output stored as unified diff […]
System Design
System Design
Learn to design scalable, reliable systems that handle millions of users. System design interviews test your ability to architect real-world applications, considering tradeoffs, scalability, and best practices.
Core Topics:
Scalability: Load balancing, horizontal vs vertical scaling
Storage: Databases (SQL vs NoSQL), caching (Redis, Memcached)
Reliability: Replication, failover, disaster recovery
Performance: CDNs, caching strategies, database indexing
Common Design Questions:
Design URL shortener (bit.ly)
Design rate limiter
Design Twitter/Instagram feed
Design messaging system (WhatsApp)
Design file storage (Dropbox)
Interview Level: Senior engineers (L5+) at FAANG companies. Requires 3-5+ years experience to tackle effectively.
Preparation: Study system design patterns, understand distributed systems fundamentals, and practice mock interviews.
System Design
Low-Level Design: Digital Library System – Catalog, Borrowing, Reservations, and DRM (2025)
Core Entities License Management Unlike physical books, digital copies can support multiple simultaneous loans up to a licensed limit. The
System Design
Low-Level Design: Recommendation Engine – Collaborative Filtering, Content-Based, and Hybrid (2025)
Core Entities and Schema The recommendation engine centers on four entities. User: user_id, preferences JSONB, created_at. Item: item_id, category, features
System Design
Low-Level Design: API Rate Limiter – Token Bucket, Sliding Window, and Distributed Throttling
Core Entities Two primary entities drive the design: Token Bucket Algorithm Tokens refill at rate r tokens/second up to capacity
System Design
Low-Level Design: Ride-Sharing Dispatch System — Matching, Routing, and Surge Pricing
Core Entities Driver: driver_id, name, vehicle_type (ECONOMY/COMFORT/XL), status (OFFLINE, AVAILABLE, ON_TRIP), current_location (POINT: lat/lng), last_location_update, rating, acceptance_rate. Rider: rider_id, name,
System Design
Low-Level Design: Social Feed System — Fan-Out, Ranking, and Personalization
Core Entities and Fan-Out Strategies Post: post_id, author_id, content, media_urls (array), created_at, like_count, comment_count, share_count. Follow: follower_id, followee_id, created_at. FeedItem:
System Design
System Design: Maps and Navigation Platform — Routing, ETA, and Real-Time Traffic (2025)
Requirements and Scale Functional: turn-by-turn navigation, ETA estimation, real-time traffic updates, points of interest search, route alternatives. Non-functional: 1B daily
System Design
Low-Level Design: Flash Sale System — Inventory Lock, Queue Fairness, and Oversell Prevention
Core Challenge and Entities A flash sale creates a sudden traffic spike (100x-1000x normal load) competing for limited inventory. The
System Design
System Design: Collaborative Document Editing — Operational Transformation and CRDT (2025)
Requirements and Core Challenge Functional: multiple users edit the same document simultaneously, changes from all users are reflected in real
System Design
System Design: Payment Processing Platform – Authorization, Settlement, and Fraud Detection (2025)
Scope and Requirements A payment processing platform handles money movement between buyers and sellers through external payment processors (Stripe, Adyen,
System Design
Low-Level Design: Content Moderation System – Rules Engine, ML Scoring, and Appeals (2025)
Problem Statement Design a content moderation system for a social platform. User-generated content (text, images, video) must be screened before
System Design
Low-Level Design: Appointment Scheduling System — Availability, Booking, and Conflict Prevention
Core Entities Provider: provider_id, name, email, type (DOCTOR, THERAPIST, CONSULTANT, TUTOR), timezone, settings (JSONB: buffer_minutes_between_appointments, max_advance_days, min_notice_hours, auto_confirm). Schedule: schedule_id,
System Design
System Design: Video Processing Platform — Upload, Transcoding, Storage, and Streaming (2025)
Requirements and Scale Functional: upload raw video, transcode to multiple resolutions (240p/480p/720p/1080p/4K), store and serve video streams, support adaptive bitrate
System Design
Low-Level Design: Warehouse Inventory Management — Stock Tracking, Reservations, and Replenishment
Core Entities Product: product_id, sku, name, category_id, unit_cost, unit_weight_grams, dimensions (JSONB: length, width, height in mm), reorder_point, reorder_quantity, lead_time_days, is_active.
System Design
Low-Level Design: IT Ticketing System — Ticket Lifecycle, SLA Tracking, and Assignment (2025)
Core Entities Ticket: ticket_id, title, description, status (OPEN, IN_PROGRESS, PENDING, RESOLVED, CLOSED), priority (P1/P2/P3/P4), category (BUG, FEATURE, INCIDENT, QUESTION, CHANGE),