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What are the key properties of Delta Lake that differentiate it from traditional data lakes?

Spark/Big Datahard0.5 min readPremium

**ACID**: Transaction log ensures atomic commits; concurrent readers see consistent snapshots. **Time Travel**: versionAsOf, timestampAsOf; audit and rollback. **Schema Enforcement/Evolution**: Reject bad data; add columns additively. **MERGE/UPDATE/DELETE**: Upserts, CDC,...

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Frequency
Low
Asked at 1 company
Category
452
questions in Spark/Big Data
Difficulty Split
88E|81M|283H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Puma

Why This Question Matters

This hard-level Spark/Big Data question appears frequently in data engineering interviews at companies like Puma. While less common, it tests deeper understanding that distinguishes strong candidates.

How to Approach This

This is a senior-level question that tests architectural thinking. Lead with the high-level design, then drill into specifics. Discuss trade-offs explicitly - there is rarely one correct answer. Show awareness of scale, fault tolerance, and operational complexity.

Expert Answer
97 words

ACID: Transaction log ensures atomic commits; concurrent readers see consistent snapshots.

Time Travel: versionAsOf, timestampAsOf; audit and rollback.

Schema Enforcement/Evolution: Reject bad data; add columns additively.

MERGE/UPDATE/DELETE: Upserts, CDC, corrections without full overwrite.

OPTIMIZE/Z-Order: Compact files; cluster by columns for read performance.

Unified Batch + Streaming: Same table for batch and streaming sink.

Why These Matter: Traditional lake = files; no transactions, no deletes, no time travel. Delta enables production use cases.

Scalability Trade-offs: Log growth; checkpoint and VACUUM. Z-order write cost.

Cost Implications: Log overhead ~5%; compaction reduces read cost. Enables CDC and late-arriving data handling.

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