Saga Pattern
saga-pattern
System Design
Distributed Transactions (2PC, Saga Pattern)
When a single business operation spans multiple services or databases, you cannot rely on a single ACID transaction. This lesson covers the two dominant patterns for keeping consistency across services: Two-Phase Commit (2PC) for synchronous, atomic, blocking transactions, and the Saga pattern (orchestration vs choreography) for long-running asynchronous workflows with compensating actions. We also cover Three-Phase Commit, idempotency keys, the outbox pattern, and the trade-offs that explain why 2PC is rare in microservices and Sagas are everywhere. By the end you can pick the right pattern for an order checkout, a money transfer, or a multi-step booking flow.
Design an E-Commerce Platform (Amazon)
Design an Amazon-scale e-commerce platform that lets 200M monthly users browse 100M SKUs, add items to a cart, check out, and have orders fulfilled from regional warehouses. The interview centerpiece is the order lifecycle: how to reserve inventory atomically while a customer is on the checkout page, how to chain cart-to-payment-to-fulfillment as a saga with compensating actions, and how to make checkout idempotent so a flaky network never charges a customer twice. We also cover catalog browse at scale, multi-warehouse fulfillment routing, and the asymmetric read/write workload that makes aggressive catalog caching the right call.
Community
A Redux + redux-saga Wiring I Still Reach For
redux-saga still earns its keep when async workflows get tangled. The wiring I copy-paste into legacy codebases, plus the takeEvery vs takeLatest decision and the canonical fetch saga.
The Saga Pattern: When Distributed Transactions Aren't an Option
Why 2PC is rarely available, what a saga actually is, and the compensation design rules that separate working sagas from stuck ones.