What is the difference between two-phase commit and saga pattern?

Question

Accepted Answer

**2PC** — distributed transaction. **Saga** — sequence of local transactions.

**Two-Phase Commit (2PC):**
- Coordinator manages transaction.
- Phase 1: Prepare (vote).
- Phase 2: Commit or Rollback.
- Strong consistency.
- Blocking, low performance.

```
2PC:
Coordinator → Prepare → Participants
Participants → Vote (Yes/No)
If all Yes → Commit
If any No → Rollback
(Strong consistency, blocking)
```

**Saga Pattern:**
- Sequence of local transactions.
- Each step has compensating action.
- Eventual consistency.
- Non-blocking, higher performance.

```
Saga:
1. CreateOrder → Success
2. ProcessPayment → Success
3. ShipOrder → Fail → Compensate: RefundPayment, CancelOrder
(Eventual consistency, non-blocking)
```

**Key differences:**
- **2PC** — strong consistency.
- **Saga** — eventual consistency.
- **2PC** — blocking.
- **Saga** — non-blocking.

Systems Analyst: What is the difference between two-phase commit and saga pattern?