TikTok System Design Questions

Design Near-Real-Time Top Songs by Country

Design a system that continuously computes the top K items from a very large event stream: for example the K most-viewed URLs, the K services with the most error logs in the last 5 minutes, the top 100 most active users in a…

Also reported as: Design Real-Time Trending Likes

Design a Data Service for Downstream Consumers

Design a service that exposes governed data-warehouse or modeled data to downstream reports and applications through stable APIs. Requirements: stable versioned data contracts, access control (row and column level), pagination…

Trace and Debug Agent Tool-Call Failures

An AI agent calls external tools; when a call fails, the visible error does not reveal whether it failed while building the request, reaching the tool, executing it, parsing the response, or during retries. Design tracing and…

Prevent a Cache Stampede on a Hot Key

Design a distributed cache (like Memcached or Redis cluster) and explain how it evolves as data volume grows and it runs across many machines. Cover partitioning with consistent hashing, replication, eviction policies,…

Evaluate a Migration from MySQL to MongoDB

A team proposes migrating an existing MySQL-backed service to MongoDB. Explain how you would decide whether the migration is justified (access patterns, schema flexibility, scaling needs, transactions and joins, consistency),…

Design An Ad Creative Relationship Processing System

Design a system that processes ad creative plans: for each advertiser plan it takes videos, keywords and other creatives, calls an external model API to compute relationships (e.g., which keywords match which video), and stores…

Design a Distributed Rate Limiter

Design a distributed rate limiter that protects APIs by limiting requests (or consumed units such as LLM billing tokens or storage quota) per user, API key, tenant, or IP. It must support configurable rules (e.g., 100…

Design an RBAC Relational Schema

Design an authorization system that supports both role-based access control (users and groups have roles such as Admin, Editor or Viewer that grant permissions) and resource-level ACLs (individual resources grant or deny specific…

Design a Synchronized Live Comment Overlay

Design a live comments system for live video (like Facebook Live or TikTok Live), or a synchronized comment overlay pinned to a video's timeline. Viewers post comments and all viewers of the stream see new comments within about a…

Model Campaigns, Targeting, and Edit History for a Demand-Side Ad Platform

Design the data model for a demand-side advertising platform where advertisers create and edit campaigns. Represent Advertiser, Campaign, Ad Group, Ad and Creative with their relationships, audience targeting criteria…

Design a Real-Time Auction Platform

Design a real-time online auction platform like eBay, or live auctions attached to social media posts. Sellers list items with a start price and end time; buyers place bids; everyone watching sees the current highest bid and bid…

In-memory file system

Design a file system abstraction: an in-memory hierarchical file system supporting mkdir, ls, create file, write/append, read and delete on paths; then discuss how to persist it so that file contents and metadata are recovered…

Design a High-Frequency Job Scheduler

Design a distributed job scheduler that runs user-defined jobs at a specified time (one-time) or on a recurring cron schedule, at a scale of millions of jobs per day. Requirements: jobs fire close to their scheduled time, each…

Design a TinyURL-like short link service

Design a URL shortening service like TinyURL or bit.ly. Users submit a long URL and get a short code (optionally a custom alias and expiry); visiting the short URL redirects to the original. Assume hundreds of millions of new…

Design a distributed key-value store

Design a horizontally scalable distributed key-value store like DynamoDB or Cassandra, or scale a single-node store to a stated workload (e.g., 50M keys, 1M requests/sec, 50/50 reads and writes). Support get/put/delete with…

Design a content moderation system

Design a content moderation system for a social platform that detects harmful content (e.g., posts or ads selling weapons, hate speech, nudity) in text, images and video. New content is scored at upload time with low latency;…

Design low-latency large-scale hotel booking system

Design a hotel or rental booking system like Booking.com or Airbnb. Users search listings by location and date range with filters, view availability and a price quote, book a room or property, and cancel; hosts manage listings,…