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Lessons (17)

• Capacity, Availability, Latency and CAP

  … a design chooses latency targets, availability targets and a partition-time consistency policy](/img/system-design-l6/capacity …

• Flash Sale: 10 Million Buyers, No Oversell

  … Never separately “check available” then decrement: concurrent requests race. Give every purchase an idempotency key, reconcile reservations/orders …

• ACID, Transactions & Locks

  … UPDATE inventory SET available = available - 1 WHERE sku = :sku AND available 0; If zero rows change, inventory was …

• Design a Ride-Sharing Service

  Match riders and drivers with a geo index, safely lease availability, and treat location as a fast-changing …

• Brokers, Replication & Durability

  … more available, but it can lose data . Keep it false for important topics.) The controller and KRaft One …

• System Design Interview Framework

  … svg) 1. Clarify users, core flows, scope, latency, availability and consistency. 2. Estimate peak RPS, storage, bandwidth and …

• What Is Software Architecture?

  … it grow? Handle 10× traffic on Black Friday Availability Is it up? 99.9% uptime Maintainability Is it …

• The L6 System-Design Thinking Loop

  … a few seconds of stale playback position to keep playback available” is stronger than “eventual consistency is fine.”

• Service Communication: Sync vs Async

  … Latencies add up, and failures cascade. Availability multiplies If each service is available 99.9% of the time …

• Indexes, EXPLAIN & Query Plans

  … Remove unused indexes carefully, and create large production indexes with the engine-safe online/concurrent method where available.

• SQL vs NoSQL Databases

  … MongoDB, etcd, HBase"] P -- A["Choose Availability (AP)<br/ answer with possibly stale data<br/ e.g. Cassandra …

• Scaling & Health Probes

  … schedule the 2 Pending pods ✅ Staying available during maintenance PodDisruptionBudget (PDB): "during voluntary disruptions (node upgrades, drains), always …

• Observability: Logs, Metrics & Traces

  … 0.1% ≈ 43 minutes of failure per month Availability Downtime per year Per month --- --- --- 99% 3.65 days …

• Scaling, Load Balancing & Rate Limiting

  … br/ max 10 tokens")] Req[Request] -- Check{token available?} Bucket -- Check Check -- yes: take 1 OK[✅ 200 OK …

• React Hooks in Practice

  … Context makes a value available to a whole subtree. jsx const ThemeContext = createContext("light"); function App() { const [theme …

• Caching & Redis

  … if (count 100) throw new TooManyRequestsError(); Persistence and availability - RDB snapshots: save the whole dataset every N minutes …

• Hexagonal Architecture (Ports & Adapters)

  … Promise<Loan { if (!(await this.catalog.isAvailable(bookId))) throw new DomainError("Book is not available"); if ((await this …