Lesson 3.3:
Distributed Data Strategies

Sharding & Horizontal Scale

When a single database server cannot handle the work, we shard. MongoDB Atlas automates the partitioning of data across shards based on a critical shard key.

Multi-Document Transactions

Even in a sharded environment, MongoDB supports ACID transactions. Use these sparingly for critical operations like financial transfers.

const session = client.startSession();
session.startTransaction();
try {
  await db.collection("accounts").updateOne({ _id: A }, { $inc: { balance: -100 } }, { session });
  await db.collection("accounts").updateOne({ _id: B }, { $inc: { balance: 100 } }, { session });
  await session.commitTransaction();
} catch (error) {
  await session.abortTransaction();
} finally {
  session.endSession();
}

Global Clusters & Low Latency

MongoDB Atlas Global Clusters allow you to place data near your users (e.g., European data in EU regions) for sub-millisecond response times across the globe.

Check Your Knowledge

What is the most important factor in a performant sharded cluster?

• Shard Key Choice
• Disk Space