How Do Multi-Document ACID Transactions Work In MongoDB?

The multi-document ACID (Atomicity, Consistency, Isolation, and Durability) transactions model in MongoDB allows developers to implement transactions over several documents within a MongoDB database, the resulting transactions are guaranteed to be atomic and consistent across documents.

• Start Transaction: To start a multi-document transaction the developer first gets the session started with the help of the method startSession() of the MongoDB driver.
• Define Operations: Within the transaction session, it is possible to determine what read and write operations the developer defines which can also go across several documents or collections. The operations can be such as insertion, updating, removal, and querying.
• Execute Operations: Once the operations are specified, the developer executes them within the transaction session. All processes conducted in the session hold the same transaction.
• Isolation: MongoDB provides the isolation of data by keeping it for separate transaction processes separately. This implies that the changes incorporated in one transaction are not obtained by other transactions until they are also committed.
• Consistency: MongoDB allows you to maintain consistency by validating or enforcing any data constraints or rules that have been defined in the database schema. Transactions, which guarantee that the database remains in a consistent state throughout running and after stopping, ensure this.
• Atomicity: In the case that any one operation within the transaction fails or encounters an error, MongoDB automatically undoes all the changes made by the same transaction. 
• Commit Transaction: When, at last, the developer is certain that all operations within the transaction session have been successfully executed without any errors, he/she can commit the transaction to the remote database by using the commitTransaction() method. 
• Rollback Transaction: In case any operation of the transaction generates an error or if the transaction is intentionally ended up by the developer, MongoDB takes care of the rollback of all the changes made by the transaction and maintains the data consistency.
• Durability: Once a transaction is committed, MongoDB ensures durability by persisting the changes made by the transaction to disk. This ensures that the changes are durable and remain intact even in the event of a system failure or crash.

MongoDB ACID transactions are fundamental for ensuring data integrity in database transactions. In MongoDB, ACID properties play a crucial role in maintaining the reliability and consistency of data operations.

In this article, We will learn about ACID transactions in MongoDB, understand their importance with examples, and see how the transaction works in MongoDB along with their use cases.