Transactions

MongoDB transactions work the same: you open a session, do several operations and commit or abort them together, even when they touch documents on different ranges and nodes.

const session = db.getMongo().startSession();
session.withTransaction(() => {
  const accounts = session.getDatabase("bank").accounts;
  accounts.updateOne({ _id: "A" }, { $inc: { balance: -100 } });
  accounts.updateOne({ _id: "B" }, { $inc: { balance: 100 } });
});

Isolation

Each transaction reads a snapshot at its read timestamp and sees its own writes. Inside a transaction, readConcern local, majority and snapshot all read that same snapshot.

How it commits

If every key of the transaction is in one range, it commits in one phase. If not, each range keeps provisional versions and a transaction record decides; cleaning up those versions continues in the background after the answer.

Limits and errors

The error labels (TransientTransactionError, UnknownTransactionCommitResult) and commit retry are MongoDB's, so the drivers' withTransaction retries what it should. transactionLifetimeLimitSeconds is 60 by default and changes with setParameter.

Causal consistency

The drivers' causal sessions work: a read with afterClusterTime sees everything the session already wrote or read, also when it goes to another replica.