What happens when a transaction is successfully committed in MongoDB?

When a transaction is successfully committed in MongoDB, all changes made within that transaction are saved. This is a fundamental characteristic of transactions in MongoDB, ensuring that they adhere to ACID properties—Atomicity, Consistency, Isolation, and Durability.

When a commit occurs, it indicates that the operations executed within the transaction have been successfully completed and that the data modifications should be made persistent in the database. This means that any insertions, updates, or deletions that were part of the transaction will become permanent and visible to other operations.

The ability to commit all changes together ensures that the database remains in a consistent state. For instance, if you are transferring money between accounts, both the deduction from one account and the addition to another must be processed together. If any part of this operation fails during execution, the whole transaction can be rolled back to keep data integrity intact.

This contrasts sharply with the other choices. A roll back of changes, saving only the first operation, or making no changes at all would undermine the purpose of transactions and the guarantees they provide for the handling of data.