Module Overview: Consistency & Trade-offs

"How consistent does it need to be?"

This module covers consistency models (strong, eventual), isolation levels, and practical correctness techniques (idempotency, versioning, transactions, sagas).

Learning Goals

• Choose consistency and isolation appropriate for the product
• Identify invariants and design around them
• Apply techniques to manage concurrency and conflicts
• Document trade-offs and assumptions explicitly

Interview Preparation

• ✅ Explain consistency vs availability trade-offs
• ✅ Discuss read-your-writes, monotonic reads, and linearizability
• ✅ Design for correctness with retries and concurrent writers

Real-World Application

• Payments and inventory correctness
• Collaborative edits and conflict resolution
• Distributed transactions and saga workflows

Estimated Time

45-60 minutes (includes practice)

Checklist

• Can name common consistency models and their impact
• Can pick isolation levels for key flows
• Can design idempotent APIs and retries