Saga pattern
Saga pattern — способ обеспечить consistency в distributed transactions без 2PC (two-phase commit). Разбивает транзакцию на локальные steps + compensation actions (отмена step'а, если следующий failed). Два стиля: choreography (events между сервисами) и orchestration (central coordinator). Popular в microservices при purchase flows: order → payment → shipping → confirm, rollback on any failure.
Ниже: подробности, пример, смежные термины, FAQ.
Подробности
- Choreography: services listen to events, react. Loose coupling, harder to debug
- Orchestration: saga orchestrator manages flow (Netflix Conductor, Temporal, AWS Step Functions)
- Compensation: каждый step имеет inverse. Payment → RefundPayment
- Idempotency: steps должны быть idempotent на retry
- Failure modes: partial completion, retry storms
Пример
Saga: PlaceOrder
1. ReserveInventory → compensation: ReleaseInventory
2. ChargePayment → compensation: RefundPayment
3. ShipOrder → compensation: CancelShipment
On failure at step 3 → run compensations 2, 1 in reverseСмежные термины
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Часто задаваемые вопросы
Saga vs 2PC?
2PC (XA transactions) — synchronous, locks ресурсы, не масштабируется, редко в cloud. Saga — async, eventual consistency, no locks.
Choreography или orchestration?
Choreography для 2-3 services. Orchestration для complex flows (5+ steps) — легче debug и modify.
Tool recommendations?
Temporal (temporal.io) — modern, durable execution. Netflix Conductor. AWS Step Functions. For simpler — just messages via Kafka/RabbitMQ.