What are MongoDB Transactions and ACID Support?

MongoDB Transactions and ACID support is a topic that plays a key role in ensuring data integrity and security in today's software projects. Traditionally, although NoSQL databases have been developed with performance and flexibility in mind, MongoDB transactions have become important due to the need for multiple operations frequently encountered in enterprise applications. Especially in critical areas such as banking and e-commerce, operations spanning multiple data collections must occur in complete consistency.

What are MongoDB Transactions?

Previously, MongoDB only supported atomic operations on a single document, but with version 4.0, it started to offer support for multi-document transactions. The concept of transactions ensures that a group of database operations either completes entirely successfully or is cancelled without any being applied. In this way, data consistency is maintained at every stage of interdependent operations, and rollback becomes possible.

Using Multi-Document Transactions in MongoDB

You can see the use of MongoDB transactions with a simple Node.js example below:

const { MongoClient } = require("mongodb");

async function runTransaction() {
  const client = new MongoClient("mongodb://localhost:27017");
  await client.connect();
  const session = client.startSession();
  const db = client.db("testdb");

  try {
    session.startTransaction();
    await db.collection("kullanici").insertOne({ isim: "Ali" }, { session });
    await db.collection("bakiye").updateOne(
      { userId: 1 },
      { $inc: { miktar: -100 } },
      { session }
    );
    await session.commitTransaction();
    console.log("Transaction completed successfully.");
  } catch (e) {
    await session.abortTransaction();
    console.error("Transaction failed:", e);
  } finally {
    await session.endSession();
    await client.close();
  }
}

runTransaction();

ACID Criteria and MongoDB

ACID is a set of features that guarantees the security and consistency of database operations:

• Atomicity: Operations work in indivisible wholes. If one of the operations within the transaction fails, all operations are rolled back.
• Consistency: The database remains consistent even after transactions.
• Isolation: Concurrent operations do not affect each other; each operation works independently.
• Durability: Successfully completed operations are stored permanently and are not lost even in system failures.

MongoDB 4.0 and later provides full ACID compliance when needed through multi-document transactions. Although standard operations do not always require ACID conditions, transaction support is indispensable for data integrity in critical applications.

Conclusion: When Should You Use Transactions?

Thanks to MongoDB Transactions and ACID support, it is now possible to perform reliable and consistent operations in NoSQL projects as well. However, in high-performance, single document-focused applications, atomic operations should be preferred instead of transactions. If you are working in a scenario where integrity across multiple collections is required, be sure to take advantage of the benefits provided by MongoDB transactions and ACID criteria.