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Lessons (20)

• Design a Chat Application

  Deliver live messages without losing them by separating durable messages from fan-out, presence and offline notifications. ![Chat …

• Design a URL Shortener

  Generate durable short links, redirect in milliseconds, prevent abuse and keep analytics off the redirect path. A short …

• Brokers, Replication & Durability

  … 62 🐢 fell behind<br/ removed from ISR"] The durability trio ⭐ These three settings together decide whether an acknowledged …

• Database Internals, Replication and Scaling

  Connect storage-engine choices, durability, replicas, query plans, pooling and data layout to real production behaviour. ![Database path …

• Design a File Storage Service

  Upload bytes directly to object storage while the API owns durable metadata, authorization, sharing and synchronization. ![File storage …

• Design a Logging and Monitoring Platform

  … agents batch into an ingestion layer, durable streams feed hot search, metrics and cold archival](/img/system-design …

• Design a Social Media Feed

  Build a fast home feed with fan-out choices, durable post storage, eventual consistency and safeguards for celebrity …

• Flash Sale: 10 Million Buyers, No Oversell

  … The durable inventory owner decides the winner atomically. The invariant Never sell more units than exist. The winner …

• Exactly-Once Payment Processing

  Safe payment retries need a durable idempotency record, atomic state transition and provider-side deduplication. The invariant For …

• Design an E-Commerce Checkout

  … inventory reservation, idempotent payment, order creation and durable events. ![Checkout: catalog/search are read paths while inventory, payment …

• What Is Apache Kafka?

  Kafka is a distributed, durable log of events that many systems can write to and read from at …

• Big Data: ETL, Warehouses and Streaming

  … raw events land durably, ETL/stream processing creates curated lake and warehouse datasets](/img/system-design-l6/big …

• Proxies, APIs and Real-Time Protocols

  … A queue is not a WebSocket, and a WebSocket is not a durable message log.

• Premiere-Night Video Streaming

  … Heartbeat progress to Redis for fast resume and persist asynchronously to durable storage. Include a timestamp/sequence so …

• Transactions, Indexes & Concurrency

  … Atomicity is all-or-nothing; consistency preserves constraints; isolation defines concurrent visibility; durability survives failure. Never wait for …

• The L6 System-Design Thinking Loop

  … Explain metrics, mitigation, and the durable fix. 💡 A good trade-off is specific: “I accept a few seconds …

• Message Queues & RabbitMQ

  … crypto.randomUUID() }, // write to disk ); js // consumer.js const channel = await connection.createChannel(); await channel.assertQueue("emails", { durable …

• ACID, Transactions & Locks

  … Two buyers cannot both reserve the last item. Durability Crash after success A committed payment record is recovered …

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … takeaways - RabbitMQ = smart routing + delete after delivery; Kafka = durable, replayable, ordered log at huge scale. - Choose Kafka for …

• Data in Microservices: Sagas & the Outbox Pattern

  … A simple orchestrator (tools like Temporal make this durable and crash-safe) async function placeOrderSaga(order) { const done …