Databricks Data Engineer Professional Question 17
Select 2You are working on a Delta Lake table in a collaborative environment. Two users attempt to write data to the same Delta table simultaneously. User A is trying to update a specific row, while User B is trying to delete the same row. How does Delta Lake's Optimistic Concurrency Control handle this scenario, and which transactions might conflict?
- A
Both transactions will succeed because Delta Lake uses versioning to maintain both updates and deletes.
- B
User A's update will succeed, but User B's delete will fail due to a conflict in modifying the same row.
- C
User B's delete will succeed, but User A's update will fail due to a conflict in modifying the same row.
- D
Neither transaction will succeed because Delta Lake's Optimistic Concurrency Control prevents simultaneous changes to the same row.
- E
The transaction that commits first will succeed, and the other transaction will fail due to a conflict in modifying the same row.
Show answer and explanation
Correct answers: B, E
Explanation
Delta Lake's Optimistic Concurrency Control ensures isolation by validating changes to the data during the commit phase. When two transactions attempt to modify the same data (e.g., one updates a row, and the other deletes the same row), a conflict arises. The first transaction to commit will succeed, while the conflicting transaction will fail. This mechanism prevents simultaneous modifications to the same data while maintaining ACID properties.
- A. Incorrect.
This is incorrect. Delta Lake does not allow conflicting changes (such as an update and a delete) on the same row to succeed simultaneously, even with versioning in place.
- B. Correct.
This is correct. Delta Lake's Optimistic Concurrency Control identifies a conflict when two transactions modify the same row. Depending on the order of execution, one transaction (in this case, the update) may succeed while the other fails.
- C. Incorrect.
This is partially correct but incomplete. While it is true that one transaction (the delete) can succeed while the other fails, this depends on the sequence of execution.
- D. Incorrect.
This is incorrect. Delta Lake does not block all operations; only the conflicting transaction fails. The unaffected transaction can still succeed.
- E. Correct.
This is correct. Delta Lake's Optimistic Concurrency Control ensures isolation by validating that no other transaction has modified the same data. The first committing transaction succeeds, while the subsequent conflicting transaction fails.