Databricks Data Engineer Professional Question 10
Select 3A data engineering team is using Delta Lake as their data storage format on cloud object storage. They want to ensure that concurrent writes to a Delta table do not corrupt the data and that committed transactions are never lost, even in the case of a system failure. How does Delta Lake guarantee these properties using its transaction log and cloud object storage?
- A
Delta Lake uses the transaction log to track all changes to the table, ensuring atomicity by maintaining a serializable order of transactions.
- B
Delta Lake stores the transaction log in memory to provide faster access, but this makes durability dependent on system uptime.
- C
Each committed transaction in Delta Lake writes an entry into the cloud object storage-backed transaction log, ensuring durability even during failures.
- D
Delta Lake uses an optimistic concurrency control mechanism to handle concurrent transactions, ensuring that only one commit is applied at a time in the transaction log.
- E
Delta Lake uses write-ahead logging (WAL) in cloud object storage to create a backup of all table versions, enabling atomicity and durability.
Show answer and explanation
Correct answers: A, C, D
Explanation
Delta Lake guarantees atomicity and durability by leveraging its transaction log and cloud object storage. The transaction log records all changes to the table and enforces a serializable order of transactions, ensuring atomicity. Cloud object storage is used to store the log, providing durability even in the event of a system failure. Additionally, Delta Lake uses optimistic concurrency control to handle concurrent transactions, ensuring that only one commit is applied at a time.
- A. Correct.
Correct: The Delta Lake transaction log records all changes to the table and ensures atomicity by enforcing a sequential order for transactions. This guarantees that either the entire operation succeeds or none of it is applied.
- B. Incorrect.
Incorrect: Delta Lake does not store the transaction log in memory; instead, it is stored in cloud object storage for durability. Storing it only in memory would make it vulnerable to system failures.
- C. Correct.
Correct: By writing the transaction log to cloud object storage, Delta Lake ensures durability since cloud storage is highly reliable and persistent. This prevents data loss during failures.
- D. Correct.
Correct: Delta Lake employs optimistic concurrency control to handle concurrent transactions. This ensures that conflicting writes are detected, and only one transaction's changes are committed to the log at a time.
- E. Incorrect.
Incorrect: Delta Lake does not use write-ahead logging (WAL). Instead, it uses the transaction log stored in cloud object storage to track table versions and ensure atomicity and durability.