Goldman Sachs System Design Questions

Design a notification system

Design a multi-channel notification service (push, email, SMS, in-app) that other services call to notify users. It must accept sudden bursts of millions of notifications with low acknowledgement latency, persist them durably,…

Also reported as: Design a notification service

Design a stock broker like Zerodha (+ LLD of order processing)

Design a stock trading or brokerage platform like Zerodha or Robinhood. Users view real-time quotes, place orders (market, limit, stop), see order status and fills, and view holdings and balances. Orders are validated (buying…

Also reported as: Simplified stock market: LLD extended to HLD

Design Pastebin

Design a Pastebin-like service where users paste text or code, receive a unique shareable link, and others can view it. Support optional expiry, public or unlisted visibility, and size limits (e.g., up to 10 MB). Expect a…

Design a Ten-Minute In-Memory Notification Deduplication Engine

Design the in-memory deduplication component of a high-throughput notification service. Each notification carries a UUID; if the same UUID arrives again within 10 minutes it must be suppressed, and after 10 minutes it may be sent…

Fix a flawed DB table: reduce redundancy, speed up lookups

You are given a database table with design flaws (redundant, denormalized columns and slow lookups). Redesign it: normalize it into appropriate tables (to 3NF), define primary and foreign keys, add indexes that speed up the…

Design a portfolio management system (HLD + DB design)

Design a portfolio management system for investors or advisors: track holdings across accounts and asset classes, record transactions (buys, sells, dividends, transfers), compute positions, P&L, allocation and performance over…

Design a URL shortener

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…

Twitter home timeline (global + follower tweets)

Design the home feed of a social network like Instagram or Twitter. Users create posts (text, photos, video), follow other users, and open a personalized feed of recent posts from people they follow, possibly mixed with global or…

Blackjack game (Ace as 1 or 11)

Design the Blackjack card game with object-oriented design: deck and shoe, cards, hands, players and dealer, dealing, hit/stand, the dealer's play rules, and determining outcomes. Handle Aces counting as 1 or 11 (compute the best…

Design an LRU cache

Design and implement an LRU cache with fixed capacity and O(1) get/put (hash map plus doubly linked list). Then extend it: make it thread-safe for concurrent reads and writes in a web service, and make it crash-resilient so the…

Design a rate limiter (code the leaky bucket)

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…

Traffic light system adapting to real-time traffic

Design a traffic light control system for an intersection that dynamically adjusts signal timings based on real-time traffic data (vehicle counts from sensors) while guaranteeing safety (no conflicting greens) and fairness…

Upload portal for internal users

Design a service that accepts large user uploads (files or product images, GBs in size), validates them, processes them asynchronously (virus scan, analysis, thumbnails, moderation), and makes results or approved assets available…