LFC Delta Lake ACID Transactions 2

Question 1

Which component of Delta Lake serves as the source of truth for all ACID transaction history?

Accepted Answer

The _delta_log transaction log directory

Answer

The _delta_log directory stores JSON commit files that record every transaction, making it the authoritative source of truth for Delta table state.

Question 2

What concurrency control mechanism does Delta Lake use to manage simultaneous write operations?

Accepted Answer

Optimistic concurrency control

Answer

Delta Lake uses optimistic concurrency control, where writers proceed without locks and conflicts are detected at commit time.

Question 3

When a Delta Lake transaction fails midway through writing Parquet files, what happens to the partially written data?

Accepted Answer

It remains as orphan files but is never referenced by the transaction log

Answer

Uncommitted Parquet files become orphan files invisible to readers; atomicity is guaranteed because the transaction log entry is only written on successful commit.

Question 4

How does Delta Lake achieve the 'I' (Isolation) property for concurrent readers during a write operation?

Accepted Answer

Readers use MVCC to access a consistent snapshot from before the write started

Answer

Delta Lake uses snapshot isolation (a form of MVCC) so readers always see a consistent, point-in-time snapshot and are never blocked by concurrent writers.

Question 5

What is the default behavior in Delta Lake when two concurrent writers attempt to modify non-overlapping partitions?

Accepted Answer

Both commits succeed because there is no conflict on the same data

Answer

Delta Lake's optimistic concurrency control allows both commits to succeed when writers touch disjoint partitions, as no actual data conflict exists.

(LFC) Lakehouse Fundamentals Certification Practice Test

(LFC) Lakehouse Fundamentals Certification Practice Test

LFC Delta Lake ACID Transactions 2