MCQs Of Day 17: MongoDB Transactions
1. Which method is used to start a MongoDB session?
A) startSession()
B) beginSession()
C) initSession()
D) openSession()
Answer: A) startSession()
Explanation: The startSession() method is used to start a new session in MongoDB.
2. What is the purpose of using a MongoDB transaction?
A) To run queries asynchronously
B) To ensure atomicity and consistency in multiple operations
C) To retrieve data faster
D) To avoid network connections
Answer: B) To ensure atomicity and consistency in multiple operations
Explanation: A transaction ensures that multiple operations either complete successfully or fail as a unit, providing atomicity and consistency.
3. What method is used to commit a MongoDB transaction?
A) commit()
B) commitTransaction()
C) endTransaction()
D) finalizeTransaction()
Answer: B) commitTransaction()
Explanation: The commitTransaction() method is used to commit a transaction in MongoDB.
4. What does the abortTransaction() method do?
A) Cancels the session
B) Terminates the MongoDB connection
C) Rolls back all operations performed during the transaction
D) Makes the transaction permanent
Answer: C) Rolls back all operations performed during the transaction
Explanation: The abortTransaction() method is used to cancel the transaction and roll back all changes made during the transaction.
5. How do you ensure a MongoDB operation runs as part of a transaction?
A) Use the session option in the operation
B) Use withTransaction() function
C) Both A and B
D) None of the above
Answer: A) Use the session option in the operation
Explanation: Operations must be performed using a session in order to be part of a transaction.
6. What happens if a MongoDB transaction encounters an error?
A) The transaction is automatically committed
B) The transaction is aborted and changes are rolled back
C) The transaction continues to run
D) The error is ignored
Answer: B) The transaction is aborted and changes are rolled back
Explanation: If an error occurs in a transaction, MongoDB automatically rolls back all changes and aborts the transaction.
7. What happens to the operations inside a MongoDB transaction when the transaction is committed?
A) Operations are discarded
B) Operations are saved permanently
C) Operations are queued for later execution
D) Operations are reverted
Answer: B) Operations are saved permanently
Explanation: Once the transaction is committed, all the changes made inside the transaction are saved permanently in the database.
8. What should be done if you want to ensure that multiple withdrawals from different accounts are processed atomically?
A) Use a single updateOne() operation
B) Use a MongoDB transaction with multiple updateOne() operations
C) Use updateMany() operation
D) Use separate sessions for each withdrawal
Answer: B) Use a MongoDB transaction with multiple updateOne() operations
Explanation: A transaction ensures that multiple operations are performed atomically. Using it for multiple withdrawals guarantees consistency.
9. What is the main advantage of using a transaction in MongoDB?
A) Faster execution of queries
B) Reduced storage requirements
C) Atomicity and consistency of operations
D) Improved indexing performance
Answer: C) Atomicity and consistency of operations
Explanation: Transactions allow multiple operations to be grouped together and ensure they succeed or fail as a unit, maintaining consistency and atomicity.
10. Which method is used to initiate a MongoDB session?
A) start()
B) session()
C) begin()
D) startSession()
Answer: D) startSession()
Explanation: The startSession() method is used to create a new session in MongoDB.
11. What happens to a MongoDB transaction if an error occurs?
A) All operations are committed
B) The transaction is rolled back
C) The operations continue regardless of the error
D) A new session is started
Answer: B) The transaction is rolled back
Explanation: If an error occurs during a transaction, MongoDB rolls back all operations to maintain data consistency.
12. How do you specify that an operation should be part of a transaction in MongoDB?
A) Using a callback function
B) Passing a session object to the operation
C) Using the session keyword in the query
D) Using a commitTransaction() method
Answer: B) Passing a session object to the operation
Explanation: Operations in a transaction require the session object to be passed as part of the operation to ensure they are executed as part of the transaction.
13. Which of the following ensures data consistency across multiple documents in MongoDB?
A) updateMany()
B) find()
C) MongoDB transactions
D) insertMany()
Answer: C) MongoDB transactions
Explanation: MongoDB transactions allow multiple document operations to be performed in an atomic and consistent manner.
14. What is the purpose of using session in MongoDB transactions?
A) To specify the operation's timeout
B) To ensure that the operation is part of a transaction
C) To optimize query performance
D) To specify the user accessing the database
Answer: B) To ensure that the operation is part of a transaction
Explanation: A session is used to track the operations within a transaction to ensure that all operations are part of the same atomic unit.
15. Which of the following methods is used to finalize the transaction and make the changes permanent in MongoDB?
A) finalizeTransaction()
B) commit()
C) commitTransaction()
D) saveTransaction()
Answer: C) commitTransaction()
Explanation: commitTransaction() is used to finalize the transaction and make the changes permanent.
16. What is the primary goal of using transactions in MongoDB?
A) To speed up queries
B) To ensure atomicity and consistency in multi-step operations
C) To reduce disk space usage
D) To create indexes on collections
Answer: B) To ensure atomicity and consistency in multi-step operations
Explanation: MongoDB transactions help in ensuring that multiple operations execute as a single unit, maintaining atomicity and consistency.
17. In MongoDB, which operation can be wrapped in a transaction?
A) insertOne()
B) updateOne()
C) deleteOne()
D) All of the above
Answer: D) All of the above
Explanation: All MongoDB operations such as insertOne(), updateOne(), and deleteOne() can be part of a transaction if executed within a session.
18. What happens if you don't use a session for MongoDB operations inside a transaction?
A) The operations will execute without being part of the transaction
B) The operations will automatically commit
C) The operations will throw an error
D) The operations will be queued for later execution
Answer: A) The operations will execute without being part of the transaction
Explanation: If you don't use a session, the operations won't be executed as part of the transaction, and the atomicity of the operations will be lost.
19. How do you ensure that a MongoDB transaction is rolled back if an error occurs?
A) Use the commitTransaction() method
B) Use the abortTransaction() method
C) Use a session object
D) Use the catch block in the try-catch structure
Answer: B) Use the abortTransaction() method
Explanation: If an error occurs, calling abortTransaction() will roll back all changes made during the transaction.
20. Which of the following is an example of an operation that could be part of a MongoDB transaction?
A) Updating a user's profile in one collection
B) Adding a product and updating inventory in two different collections
C) Both A and B
D) None of the above
Answer: C) Both A and B
Explanation: Both operations can be part of a transaction, ensuring data consistency across collections.
21. When a MongoDB transaction is successful, what happens?
A) All changes are reverted
B) All changes are committed and made permanent
C) Only the first operation is saved
D) A backup of the database is created
Answer: B) All changes are committed and made permanent
Explanation: Once the transaction is committed, all changes made during the transaction become permanent.
22. What must be done before starting a MongoDB transaction?
A) Initialize a session
B) Commit previous transactions
C) Open a connection to the database
D) None of the above
Answer: A) Initialize a session
Explanation: A session must be started before a MongoDB transaction can begin.
23. How do you perform a multi-document update in a MongoDB transaction?
A) Use updateMany() without a session
B) Use updateMany() with a session
C) Use updateOne() for each document
D) Use insertMany() with a session
Answer: B) Use updateMany() with a session
Explanation: The updateMany() operation can be used within a transaction by passing the session to ensure all documents are updated atomically.
24. What is a consequence of failing to commit a MongoDB transaction?
A) The database will throw an error
B) The changes will be lost
C) The changes will be saved automatically
D) The database will roll back the transaction
Answer: B) The changes will be lost
Explanation: If a transaction is not committed, all the changes made during the transaction will be lost.
25. How do MongoDB transactions guarantee data consistency?
A) By updating data in a sequential manner
B) By performing all operations atomically
C) By locking the database during the transaction
D) By reducing database size
Answer: B) By performing all operations atomically
Explanation: Transactions ensure that either all operations succeed or none of them do, maintaining data consistency across multiple documents.
26. What does the withTransaction() method in MongoDB do?
A) Commits the transaction automatically
B) Starts a session for the transaction
C) Wraps the transaction logic to handle commit or rollback automatically
D) None of the above
Answer: C) Wraps the transaction logic to handle commit or rollback automatically
Explanation: The withTransaction() method handles the entire transaction process, including commit or rollback, simplifying transaction management.
27. What is the impact of using MongoDB transactions for a large number of operations?
A) Increased query performance
B) Increased memory consumption and overhead
C) Reduced network traffic
D) Faster data retrieval
Answer: B) Increased memory consumption and overhead
Explanation: Transactions can increase overhead as they require additional resources, such as memory and session management.
28. Which type of MongoDB operation is supported within a transaction?
A) Aggregation queries
B) Map-reduce operations
C) CRUD operations
D) Text searches
Answer: C) CRUD operations
Explanation: MongoDB transactions support basic CRUD operations like insert, update, and delete.
29. Which of the following is a requirement for MongoDB transactions in replica sets?
A) Transactions only work on primary replicas
B) Transactions only work on secondary replicas
C) Transactions require sharded clusters
D) Transactions require journaling to be disabled
Answer: A) Transactions only work on primary replicas
Explanation: In replica sets, MongoDB transactions can only be performed on the primary replica.
30. What is a limitation of MongoDB transactions in sharded clusters?
A) Transactions are only allowed on the primary shard
B) Transactions across multiple shards are not supported
C) Transactions require all shards to be active
D) Transactions are slower in sharded clusters
Answer: D) Transactions are slower in sharded clusters
Explanation: Transactions across multiple shards in a sharded cluster can introduce additional latency due to the complexity of coordinating across shards.
31. How does MongoDB handle isolation in transactions?
A) MongoDB provides full isolation, allowing multiple transactions to execute concurrently
B) MongoDB supports snapshot isolation but not serializable isolation
C) MongoDB provides serializable isolation only
D) MongoDB does not support isolation in transactions
Answer: B) MongoDB supports snapshot isolation but not serializable isolation
Explanation: MongoDB provides snapshot isolation, meaning it guarantees that a transaction sees a consistent view of data without being affected by other transactions.
32. How long does a MongoDB transaction remain active?
A) Until the next query is executed
B) Until the session is closed or the transaction is committed/aborted
C) 5 minutes by default
D) Until a manual timeout is set
Answer: B) Until the session is closed or the transaction is committed/aborted
Explanation: A transaction remains active until it is either committed or aborted, or the session is closed.
33. What is the role of the abortTransaction() method?
A) To finalize the changes
B) To restart the transaction
C) To roll back any changes made during the transaction
D) To save the changes to the database
Answer: C) To roll back any changes made during the transaction
Explanation: The abortTransaction() method is used to cancel the transaction and undo any changes that occurred during the transaction.
34. What happens when you don't use commitTransaction() after starting a MongoDB transaction?
A) MongoDB will automatically commit the transaction
B) The changes will be lost
C) The transaction will be rolled back automatically
D) The session will be terminated
Answer: B) The changes will be lost
Explanation: If you don't call commitTransaction(), MongoDB will discard any changes made during the transaction.
35. How do you track changes made within a MongoDB transaction?
A) Using a log() method
B) Using a session object to track operations
C) Using audit logs
D) Using custom application logic
Answer: B) Using a session object to track operations
Explanation: MongoDB tracks changes through the session object, which ensures that all operations are part of the same transaction.
36. What is the maximum duration a MongoDB transaction can be active?
A) 30 seconds
B) 1 hour
C) Until the session ends
D) No limit
Answer: C) Until the session ends
Explanation: A transaction remains active until it is either committed or aborted, or until the session ends.
37. What is the correct order of steps to perform a transaction in MongoDB?
A) Start session → Perform operations → Commit or Abort
B) Start session → Commit → Perform operations
C) Perform operations → Commit → Start session
D) Perform operations → Abort → Start session
Answer: A) Start session → Perform operations → Commit or Abort
Explanation: The correct order involves starting a session, performing the operations, and then either committing or aborting the transaction.
38. Which of the following methods is part of the MongoDB transaction lifecycle?
A) commitTransaction()
B) rollbackTransaction()
C) finalizeTransaction()
D) terminateTransaction()
Answer: A) commitTransaction()
Explanation: commitTransaction() is used to complete the transaction and save all changes made during the transaction.
39. What happens if a MongoDB transaction exceeds the allowed timeout period?
A) The transaction is automatically committed
B) The transaction is aborted and rolled back
C) The operation continues as usual
D) A new session is created
Answer: B) The transaction is aborted and rolled back
Explanation: If a transaction exceeds the allowed timeout period, MongoDB automatically aborts it and rolls back any changes made.
40. In a MongoDB transaction, what happens if one operation fails?
A) The entire transaction is committed
B) Only the failed operation is rolled back
C) The entire transaction is rolled back
D) The database crashes
Answer: C) The entire transaction is rolled back
Explanation: If any operation fails within a transaction, MongoDB will roll back all changes made during that transaction.
41. How can you handle a failure during a MongoDB transaction?
A) By catching the error and calling abortTransaction()
B) By using the rollbackTransaction() method
C) By retrying the operation manually
D) By ignoring the error and continuing with the operation
Answer: A) By catching the error and calling abortTransaction()
Explanation: If a failure occurs, you can catch the error and use abortTransaction() to roll back the changes.
42. Which of the following is true regarding MongoDB transactions?
A) They are supported only in replica sets
B) They can be used for both single and multi-document operations
C) They support serializable isolation
D) They do not support multi-document transactions
Answer: B) They can be used for both single and multi-document operations
Explanation: MongoDB transactions can be used for both single and multi-document operations.
43. What is a transaction's isolation level in MongoDB?
A) Serializable isolation
B) Snapshot isolation
C) Repeatable read isolation
D) Read committed isolation
Answer: B) Snapshot isolation
Explanation: MongoDB transactions use snapshot isolation to ensure consistent views of data across multiple operations.
44. What can MongoDB transactions help prevent in a database?
A) Indexing issues
B) Deadlock situations
C) Data inconsistency
D) Query errors
Answer: C) Data inconsistency
Explanation: MongoDB transactions help prevent data inconsistency by ensuring atomicity and consistency across multiple operations.
45. How are MongoDB transactions different from single operations?
A) Transactions provide automatic commit for all operations
B) Transactions provide atomicity across multiple operations
C) Transactions execute faster than single operations
D) Transactions are not supported for updates
Answer: B) Transactions provide atomicity across multiple operations
Explanation: Transactions ensure that multiple operations are treated as a single unit, with atomicity and consistency guarantees.
46. What is the effect of aborting a transaction in MongoDB?
A) All changes made during the transaction are saved
B) Only the last change is rolled back
C) All changes made during the transaction are undone
D) The transaction is committed automatically
Answer: C) All changes made during the transaction are undone
Explanation: Aborting a transaction undoes all changes made during the transaction, rolling back to the state before the transaction started.
47. How do you initiate a MongoDB transaction?
A) By using the startTransaction() method
B) By using the beginTransaction() method
C) By creating a session and calling startSession()
D) By executing the beginTransaction() operation
Answer: C) By creating a session and calling startSession()
Explanation: A transaction is initiated by creating a session and calling the startSession() method.
48. Which of the following is true regarding MongoDB transactions in sharded clusters?
A) Transactions are faster in sharded clusters
B) Transactions across shards can be complex and slower
C) Transactions only work on the primary shard
D) MongoDB does not support transactions in sharded clusters
Answer: B) Transactions across shards can be complex and slower
Explanation: Transactions involving multiple shards in a sharded cluster can introduce additional complexity and slower performance.
49. Which method is used to finalize and save a transaction in MongoDB?
A) commitTransaction()
B) endTransaction()
C) finishTransaction()
D) saveTransaction()
Answer: A) commitTransaction()
Explanation: The commitTransaction() method is used to finalize the transaction and save the changes made during the transaction.
50. Which method would you use to cancel a transaction and discard changes in MongoDB?
A) cancelTransaction()
B) abortTransaction()
C) discardTransaction()
D) rollbackTransaction()
Answer: B) abortTransaction()
Explanation: The abortTransaction() method is used to cancel the transaction and undo any changes made during it.
