Distributed Transactions in Node.js

1. Introduction

Distributed transactions are essential when data is spread across multiple systems or services. This lesson covers how to manage distributed transactions in Node.js effectively.

2. Key Concepts

**Distributed Transaction**: A transaction that involves multiple resources (databases, services).
**Atomicity**: Ensures that all parts of a transaction are completed successfully, or none at all.
**Consistency**: Ensures that a transaction brings the system from one valid state to another valid state.
**Isolation**: Ensures that transactions do not affect each other concurrently.
**Durability**: Guarantees that once a transaction has been committed, it will remain so, even in case of system failure.

3. Transaction Models

Two popular models for managing distributed transactions are:

**Two-Phase Commit (2PC)**: A blocking protocol that ensures all participants commit or rollback changes.
**Event Sourcing**: A non-blocking approach that uses events to track changes, allowing eventual consistency.

4. Implementing Distributed Transactions

Here's a basic example of implementing a distributed transaction using a two-phase commit approach with Node.js and PostgreSQL:

const { Client } = require('pg');

async function distributedTransaction() {
    const client1 = new Client({ connectionString: 'postgres://user:password@localhost/db1' });
    const client2 = new Client({ connectionString: 'postgres://user:password@localhost/db2' });
    
    await client1.connect();
    await client2.connect();

    try {
        await client1.query('BEGIN');
        await client2.query('BEGIN');

        // Perform operations on both clients
        await client1.query('INSERT INTO table1 (column) VALUES ($1)', ['value1']);
        await client2.query('INSERT INTO table2 (column) VALUES ($1)', ['value2']);

        await client1.query('COMMIT');
        await client2.query('COMMIT');
    } catch (error) {
        await client1.query('ROLLBACK');
        await client2.query('ROLLBACK');
        console.error('Transaction failed:', error);
    } finally {
        await client1.end();
        await client2.end();
    }
}

distributedTransaction();

5. Best Practices

Use distributed transaction protocols carefully to avoid blocking issues.
Consider eventual consistency where appropriate, as it can improve performance.
Implement proper error handling and logging for transaction failures.
Use libraries like sequelize or typeORM that support transactions natively.

6. FAQ

What is a distributed transaction?

A distributed transaction is a transaction that spans multiple databases or services, ensuring data integrity across systems.

Why use two-phase commit?

Two-phase commit ensures that either all parts of a distributed transaction are committed or none are, maintaining atomicity.

What are the downsides of distributed transactions?

Distributed transactions can introduce latency and complexity, as well as the potential for blocking behavior.