MongoDB MongoDB Transactions and ACID Compliance

Question 1

In which MongoDB version were multi-document ACID transactions introduced for replica sets?

Accepted Answer

MongoDB 4.0

Answer

Multi-document ACID transactions for replica sets were introduced in MongoDB 4.0. MongoDB 4.2 extended transactions to sharded clusters. Prior to 4.0, atomicity was guaranteed only at the single-document level.

Question 2

What does ACID stand for in the context of database transactions?

Accepted Answer

Atomic, Consistent, Isolated, Durable

Answer

ACID stands for Atomicity (all operations succeed or all are rolled back), Consistency (data moves from one valid state to another), Isolation (concurrent transactions don't interfere), and Durability (committed transactions persist even after system failure).

Question 3

How do you start a multi-document transaction in MongoDB using the Node.js driver?

Accepted Answer

session.startTransaction()

Answer

To use multi-document transactions in MongoDB, you first start a client session with client.startSession(), then call session.startTransaction(). All operations within the transaction must pass the session object, and you call session.commitTransaction() or session.abortTransaction() to finalize.

Question 4

What happens to a MongoDB transaction if commitTransaction() is not called before the session times out?

Accepted Answer

The transaction is rolled back and all changes are discarded

Answer

If a transaction is not committed before the session or transaction timeout (default 60 seconds), MongoDB automatically aborts and rolls back the transaction. All write operations within the transaction are discarded as if they never occurred.

Question 5

Which read concern is required to read the latest majority-committed data within a MongoDB transaction?

Accepted Answer

snapshot

Answer

Transactions default to 'snapshot' read concern, which provides a consistent snapshot of the data as of the transaction's start time. 'snapshot' read concern ensures that all reads within a transaction see the same consistent view of the data.

MongoDB Practice Test

MongoDB Practice Test

MongoDB MongoDB Transactions and ACID Compliance