System Design 14 - Distributed Transactions: The Art of Juggling Consistency Across Systems

#systemdesign #distributedsystems #transactions

Intro:

Distributed transactions ensure that operations spanning multiple systems are either fully completed or fully rolled back, maintaining data integrity. It’s the glue holding multi-service architectures together when consistency is critical.

1. What’s a Distributed Transaction? Coordinating Across Multiple Nodes

Purpose: Ensures all operations in a transaction succeed or fail together, even when spread across different databases or services.
Analogy: It’s like a group of friends ordering food—either everyone gets their meal, or the whole order is canceled.

2. Distributed Transaction Protocols

Two-Phase Commit (2PC): A coordinator ensures all parties agree before committing.
- Steps:
- Prepare phase: Participants signal readiness.
- Commit phase: Finalizes the transaction.
- Drawback: Can be slow due to waiting for confirmations.
Three-Phase Commit (3PC): Adds an additional phase for better fault tolerance.
Saga Pattern: Breaks a transaction into a series of smaller steps with compensating actions for rollbacks.
- Example: Booking a flight and hotel—if one fails, the other is canceled.

3. Benefits of Distributed Transactions

Data Consistency: Keeps all systems in sync, preventing partial updates.
Resilience: Ensures systems recover gracefully from failures.
Supports Complex Workflows: Ideal for multi-step, multi-service operations.

4. Real-World Use Cases

E-Commerce Checkouts: Ensures payment, inventory deduction, and order creation succeed together.
Banking Systems: Transfers across accounts in different databases require atomicity.
Travel Bookings: Coordinates reservations across flights, hotels, and rentals.

5. Challenges and Pitfalls

Performance Overhead: Increases latency due to multiple coordination steps.
Network Failures: Communication issues can lead to incomplete transactions.
Scalability: High coordination requirements can bottleneck large-scale systems.

6. Tools for Implementing Distributed Transactions

Databases:
- MySQL/InnoDB: Supports 2PC.
- CockroachDB: Provides distributed transaction support natively.
Message Brokers:
- Kafka: Implements event-driven sagas.
- RabbitMQ: Helps coordinate transactional workflows.
Libraries:
- Axon Framework (Java): Saga-based transactions.
- NestJS CQRS Module (Node.js): Saga orchestration.

Closing Tip: Distributed transactions are critical for multi-service systems needing strong consistency. Choosing between 2PC, 3PC, or sagas depends on your app’s need for speed and fault tolerance.

Cheers🥂