Databricks Data Engineer Professional Question 14
Select 2In a Delta Lake table, two transactions are executed concurrently: Transaction A writes new rows to the table, while Transaction B updates existing rows. Both transactions succeed in acquiring their initial snapshots of the table. Which scenario would lead to a conflict being detected under Delta Lake's Optimistic Concurrency Control (OCC)?
- A
Transaction A writes rows that overlap with the rows updated by Transaction B.
- B
Transaction A writes rows to a different partition than the rows updated by Transaction B.
- C
Transaction B updates rows that were added by Transaction A after Transaction B's snapshot was taken.
- D
Transaction A writes rows to the same partition as the rows updated by Transaction B, but no overlapping rows are affected.
- E
Transaction A and Transaction B modify completely different rows in the same table.
Show answer and explanation
Correct answers: A, C
Explanation
Delta Lake's Optimistic Concurrency Control ensures isolation by validating that a transaction's changes do not conflict with other concurrent transactions. Conflicts are detected when two transactions modify overlapping rows or when one transaction modifies data that another transaction added or updated after its snapshot was taken. Non-overlapping changes, even within the same partition, or changes to separate partitions do not result in conflicts.
- A. Correct.
This scenario leads to a conflict because both transactions are modifying overlapping rows, violating Delta Lake's isolation guarantees.
- B. Incorrect.
This scenario does not lead to a conflict because the two transactions are working on different partitions, ensuring no overlapping data is modified.
- C. Correct.
This scenario leads to a conflict because Transaction B's snapshot does not include the rows added by Transaction A, and the modifications by Transaction B could invalidate Transaction A's changes.
- D. Incorrect.
This scenario does not lead to a conflict because although the transactions operate on the same partition, they affect non-overlapping rows, so Delta Lake's OCC allows both transactions to succeed.
- E. Incorrect.
This scenario does not lead to a conflict because the transactions modify completely different rows, ensuring there is no overlap or invalidation of changes.