---
title: "Module Overview: Consistency & Trade-offs"
weight: 0
summary: "Consistency models, isolation, and correctness under concurrency."
---

# 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
