How MongoDB 4.0 Brings ACID Multi‑Document Transactions to NoSQL

Background

Transactions are crucial for ensuring strong data consistency in any database, and different databases implement them differently.

In relational databases, entity data spans multiple rows and tables, so transactions must span tables and rows.

In document databases, a document can contain subdocuments and arrays, allowing related data to be handled within a single document; single‑document updates are atomic and can emulate multi‑table transactions of relational databases.

According to a MongoDB survey, 80%‑90% of applications do not need multi‑document transactions, yet the relational mindset persists among developers and DBAs, and some scenarios truly require them, prompting MongoDB to plan this feature.

MongoDB began work on this three years ago, but implementation is complex, involving storage engine, protocol, sharding architecture, consistency, and high availability.

MongoDB 4.0

Finally, MongoDB 4.0 will support multi‑document transactions, scheduled for release in the summer of 2018.

This is significant because it gives MongoDB ACID guarantees comparable to relational databases while retaining its speed, flexibility, and scalability.

Multi‑document transactions make it easier for developers to handle various MongoDB use cases, and many feel reassured simply knowing MongoDB now supports robust transactions.

MongoDB’s transaction usage is similar to relational databases; an example is shown below.

Summary

MongoDB 4.0 transactions work well in a single replica set, and MongoDB 4.2 will add support for sharded deployments.