MongoDB Transactions

MongoDB transactions let several operations across multiple documents or collections succeed or fail together. Single-document writes are always atomic in MongoDB, so you only need a transaction when one business action touches more than one document.

Transactions require a replica set or sharded cluster (Atlas clusters are replica sets).

A Transaction in mongosh

Start a session, start a transaction, use the session's database handle, then commit or abort.

const session = db.getMongo().startSession()
const shop = session.getDatabase("shop")
session.startTransaction()
try {
  shop.orders.insertOne({ orderNo: 111, product: "Olive Oil", qty: 5 })
  shop.products.updateOne({ name: "Olive Oil" }, { $inc: { stock: -5 } })
  session.commitTransaction()
  print("committed")
} catch (e) {
  session.abortTransaction()
  print("aborted: " + e.message)
} finally {
  session.endSession()
}

committed

withTransaction in Node.js

Drivers offer withTransaction, which also retries on transient errors automatically.

await session.withTransaction(async () => {
  await orders.insertOne({ orderNo: 112, qty: 2 }, { session })
  await products.updateOne({ name: "Honey" }, { $inc: { stock: -2 } }, { session })
})
console.log('done')

done

Best Practices

• Prefer schema designs where one document holds the data that must change together
• Keep transactions short; the default time limit is 60 seconds
• Pass the session to every operation inside the transaction
• Handle TransientTransactionError by retrying

Frequently asked questions

Does MongoDB support ACID transactions?

Yes. Since 4.0 for replica sets and 4.2 for sharded clusters, MongoDB supports multi-document ACID transactions.

Why do I get "Transaction numbers are only allowed on a replica set"?

Your server runs standalone. Start it as a single-node replica set (--replSet rs0 then rs.initiate()) or use Atlas.

Are MongoDB transactions slow?

They add overhead compared to single-document writes, so use them only when needed. For most operations a well-designed document makes them unnecessary.