MongoDB MongoDB Transactions and ACID Compliance 2

Question 1

What is a transient transaction error in MongoDB and how should it be handled?

Accepted Answer

A temporary error (e.g., write conflict or network issue) that can be resolved by retrying the entire transaction

Answer

Transient transaction errors (ErrorLabel: 'TransientTransactionError') indicate temporary conditions like write conflicts or network issues. The application should catch these errors and retry the entire transaction from the beginning, as the original transaction was rolled back.

Question 2

What is a write conflict in a MongoDB transaction?

Accepted Answer

When two concurrent transactions attempt to modify the same document simultaneously

Answer

A write conflict occurs when two concurrent transactions attempt to write to the same document. MongoDB detects this and aborts one of the conflicting transactions with a TransientTransactionError, expecting the application to retry the aborted transaction.

Question 3

Which of the following operations CANNOT be performed inside a MongoDB multi-document transaction?

Accepted Answer

Creating a new collection or index

Answer

DDL operations such as creating collections, dropping collections, or creating indexes cannot be performed inside a multi-document transaction. Transactions are limited to DML operations (insert, update, delete, find) on existing collections.

Question 4

What is the default transaction timeout limit in MongoDB?

Accepted Answer

60 seconds

Answer

MongoDB transactions have a default timeout of 60 seconds (configurable via transactionLifetimeLimitSeconds). Transactions running longer than this limit are automatically aborted. Long-running transactions should be avoided as they hold locks and impact performance.

Question 5

In MongoDB, single-document operations are atomic by default. What does this mean?

Accepted Answer

An update to a single document either fully succeeds or fully fails — partial updates never occur

Answer

MongoDB guarantees atomicity at the single-document level without needing transactions. An operation modifying a single document (including updating multiple fields or embedded arrays) either applies all changes or none — observers never see a partial update.

MongoDB Practice Test

MongoDB Practice Test

MongoDB MongoDB Transactions and ACID Compliance 2